Add a few edit-related addons to codemirror
Add a few edit-related addons to codemirror

Change-Id: Ifc7b92623e362ca21f99022fd701982ba686a920

GerritCodeReview/plugins_codemirror-editor,GerritCodeReview/plugins_codemirror-editor,GerritCodeReview/plugins_codemirror-editor