add back the search bar
extent get_content_cache to return content kinds of a specific type
extend node_cache to add in other kinds that we want
remove unused functions in search autocomplete js
First pass fix for search_autocomplete to interact with new sidebar.
TODO: Refactor in Backbone and remove arbitrary hardcode.
Merge branch 'develop' into search

Conflicts:
	kalite/distributed/static/css/distributed/khan-lite.css
	kalite/topic_tools/__init__.py
Adds search by keyword.
Revert content cache changes.
Reinstates CONTENT global default value to None.
Removes legacy code.
Fixes icon font rendering on all pages.
Merge pull request #2527 from aronasorman/search

Reinstate Search Functionality
Merge branch 'develop' of github.com:learningequality/ka-lite into nav-polish

Conflicts:
	kalite/distributed/hbtemplates/topics/sidebar-entry.handlebars
	kalite/distributed/static/css/distributed/sidebar.css
	kalite/distributed/templates/distributed/base.html
	kalite/distributed/templates/distributed/topic.html