SONAR-1792: Add description for properties

subprojects/sonar-dev-maven-plugin/src/main/scripts/dev.mojos.xml

   <mojos>
     <mojo>
       <goal>start</goal>
-      <description></description>
+      <description>Start Sonar.</description>
       <call>start</call>
       <requiresProject>false</requiresProject>
       <parameters>
         </parameter>
         <parameter>
           <name>pluginArtifact</name>
-          <description></description>
+          <description>Plugin to install.</description>
           <property>pluginArtifact</property>
           <expression>${sonar.pluginArtifact}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>extensionsDir</name>
-          <description></description>
+          <description>Directory from where extensions should be copied.</description>
           <property>extensionsDir</property>
           <expression>${sonar.extensionsDir}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>background</name>
-          <description></description>
+          <description>Set to true to run Sonar in background mode.</description>
           <property>background</property>
           <expression>${sonar.background}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>clean</name>
-          <description></description>
+          <description>Set to false to prevent clean installation.</description>
           <property>clean</property>
           <expression>${sonar.clean}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>localRepository</name>
-          <description></description>
+          <description>Local Maven repository.</description>
           <property>localRepository</property>
           <expression>${settings.localRepository}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>configBackup</name>
-          <description></description>
+          <description>File from where Sonar configuration should be restored.</description>
           <property>configBackup</property>
           <expression>${sonar.configBackup}</expression>
           <required>false</required>
 
     <mojo>
       <goal>stop</goal>
-      <description></description>
+      <description>Stop Sonar.</description>
       <call>stop</call>
       <requiresProject>false</requiresProject>
       <parameters>
 
     <mojo>
       <goal>start-war</goal>
-      <description></description>
+      <description>Starts Sonar WAR.</description>
       <call>start-war</call>
       <requiresProject>false</requiresProject>
       <parameters>
         </parameter>
         <parameter>
           <name>pluginArtifact</name>
-          <description></description>
+          <description>Plugin to install.</description>
           <property>pluginArtifact</property>
           <expression>${sonar.pluginArtifact}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>extensionsDir</name>
-          <description></description>
+          <description>Directory from where extensions should be copied.</description>
           <property>extensionsDir</property>
           <expression>${sonar.extensionsDir}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>background</name>
-          <description></description>
+          <description>Set to true to run Sonar in background mode.</description>
           <property>background</property>
           <expression>${sonar.background}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>clean</name>
-          <description></description>
+          <description>Set to false to prevent clean installation.</description>
           <property>clean</property>
           <expression>${sonar.clean}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>localRepository</name>
-          <description></description>
+          <description>Local Maven repository.</description>
           <property>localRepository</property>
           <expression>${settings.localRepository}</expression>
           <required>false</required>
         </parameter>
         <parameter>
           <name>configBackup</name>
-          <description></description>
+          <description>File from where Sonar configuration should be restored.</description>
           <property>configBackup</property>
           <expression>${sonar.configBackup}</expression>
           <required>false</required>
 
     <mojo>
       <goal>stop-war</goal>
-      <description></description>
+      <description>Stops Sonar WAR.</description>
       <call>stop-war</call>
       <requiresProject>false</requiresProject>
       <parameters>
 
     <mojo>
       <goal>analyze</goal>
-      <description></description>
+      <description>Analyzes projects using Sonar.</description>
       <call>analyze</call>
       <requiresProject>false</requiresProject>
       <parameters>
         </parameter>
         <parameter>
           <name>projectsDir</name>
-          <description></description>
+          <description>Directory containing projects.</description>
           <property>projectsDir</property>
           <expression>${sonar.projectsDir}</expression>
           <required>true</required>