Enable maven site generation for jgit

Enable maven site generation for jgit

Generating the site:
$ mvn site:site

Local staging of the site:
$ mvn site:stage
the site is staged under ./target/staging/

If you can connect to build.eclipse.org over ssh
(ask webmaster if you are a committer and need ssh access)
you can deploy a local build of the site:
$ mvn site:deploy
The site is deployed under
http://download.eclipse.org/jgit/site/${project.version}

To select the ssh key to use for deploying over ssh add the following
section to your Maven settings.xml:
<server>
  <id>jgit.website</id>
  <username>username</username>
  <privateKey>${user.home}/.ssh/id_rsa</privateKey>
  <filePermissions>664</filePermission>
  <directoryPermissions>775</directoryPermissions>
  <configuration></configuration>
</server>

To deploy the site from Hudson https://hudson.eclipse.org/egit/
enable the Maven profile "build-server".

Change-Id: I7e64c8560ca75196d2232f111ffad953c14f013f
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>
(cherry picked from commit 6d00f0a09c67421d4ac9960c568f9c18ceb4a6a4)