SideBySide: Make cursor blink rate customizable

Now, that we migrated diff user preferences to Git backend, we can
easily introduce one of the most wanted customization option: blinking
cursor.

Set default to 0: no blinking cursor, to be backwards compatible.

Change-Id: I40a3a43ea7636508f45badc4946d2f2455adb192

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

@@ -195,6 +195,12 @@ limitations under the License.
             alignment='RIGHT'/>
           or <g:CheckBox ui:field='contextEntireFile'>entire file</g:CheckBox></ui:msg></td>
       </tr>
+      <tr>
+        <th><ui:msg>Cursor Blink Rate</ui:msg></th>
+        <td><x:NpIntTextBox ui:field='cursorBlinkRate'
+            visibleLength='4'
+            alignment='RIGHT'/></td>
+      </tr>
       <tr>
         <th><ui:msg>Intraline Difference</ui:msg></th>
         <td><g:ToggleButton ui:field='intralineDifference'>