Docs fixes and enlarge tolerance

documentation/components/components-overview.asciidoc

 ((("[classname]#AbstractListing#")))
 There are three more specific types of components.
 
-<<components-fields#components.fields,"Field Components">>.
+Field Components:: allow user to edit a value in the UI. All extend [classname]#AbstractField#. Field components are described in detail in <<components-fields#components.fields,"Field Components">>.
 
 Selection Component:: show a list of data that the user can select from. All extend [classname]#AbstractListing#. Selection components are described in detail in
 <<components-selection#components.selection,"Selection Components">>.

uitest/src/test/java/com/vaadin/tests/components/grid/AbstractGridColumnAutoWidthTest.java

 @TestCategory("grid")
 public abstract class AbstractGridColumnAutoWidthTest extends MultiBrowserTest {
 
-    public static final int TOTAL_MARGIN_PX = 21;
+    public static final int TOTAL_MARGIN_PX = 26;
+    private static final int tolerance = 10;
 
     @Before
     public void before() {
         assertLessThan("header should've been narrower than body", headerWidth,
                 bodyWidth);
         assertEquals("column should've been roughly as wide as the body",
-                bodyWidth, colWidth, 5);
+                bodyWidth, colWidth, tolerance);
     }
 
     @Test
         assertGreater("header should've been wider than body", headerWidth,
                 bodyWidth);
         assertEquals("column should've been roughly as wide as the header",
-                headerWidth, colWidth, 5);
-
+                headerWidth, colWidth, tolerance);
     }
 
     @Test