SideBySide: Allow to activate match brackets Codemirror addon

Now, that we migrated diff user preferences to Git backend, we can
make activation of codemirror option: "highlight matched brackets"
customizable.

Change-Id: I37c1c1ee13ff872e3cbc349a7c9fee636312402e

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.ui.xml

@@ -289,6 +289,13 @@ limitations under the License.
           <g:downFace><ui:msg>Slow</ui:msg></g:downFace>
         </g:ToggleButton></td>
       </tr>
+      <tr>
+        <th><ui:msg>Match Brackets</ui:msg></th>
+        <td><g:ToggleButton ui:field='matchBrackets'>
+          <g:upFace><ui:msg>Off</ui:msg></g:upFace>
+          <g:downFace><ui:msg>On</ui:msg></g:downFace>
+        </g:ToggleButton></td>
+      </tr>
       <tr>
         <td></td>
         <td>