Initial implementation of the feature diff panel.  Select a commit in the history panel then right click the panel and press the "show diff" button to show the changes made in the selected commit.
Right clicking on a feature in the diff panel will now give the user an option to zoom to that feature's location.
Merge branch 'FeatureDiffPanel'

Conflicts:
	webapp/src/app/app.js
	webapp/src/app/salamati/locale/en.js
	webapp/src/app/salamati/locale/es.js
	webapp/src/gxp/script/plugins/GeoGitHistory.js
Added Feature Diff Panel.

Added Feature Diff panel that shows attribute differences in a feature between two commits. Updated grid css some so that the font in the cells are smaller, still needs some more work. Updated some hard coded strings to i18n.
Merge commit '3868b39dee2cbdac3099ad84ba4e2537798a24af'

Conflicts:
	webapp/src/app/app.js
Forgot to commit sorting of commit ids for feature diffing.