Starting to implement side-by-side diff.

Including the mark-selection addon from CodeMirror.
Adding more API wrappers to CodeMirror to support line formatting.
Adding line coloring and padding for inserts and deletes to CodeMirrorDemo.

Change-Id: I0a96506166de8e9dc32241b21d99cce9a3890fad
diff --git a/gerrit-gwtui/src/main/java/net/codemirror/CodeMirror.gwt.xml b/gerrit-gwtui/src/main/java/net/codemirror/CodeMirror.gwt.xml
index 64ac16d..a3641a553 100644
--- a/gerrit-gwtui/src/main/java/net/codemirror/CodeMirror.gwt.xml
+++ b/gerrit-gwtui/src/main/java/net/codemirror/CodeMirror.gwt.xml
@@ -16,6 +16,7 @@
 <module>
   <inherits name='com.google.gwt.logging.Logging'/>
   <inherits name='com.google.gwt.resources.Resources'/>
+  <source path='addon'/>
   <source path='lib'/>
   <source path='mode'/>
 </module>