Filtering for assets table
SOL-20 adding type filter with some deafult values
SOL-20 basic testing
cleanup of asset urls on studio assets page

Conflicts:
	cms/templates/js/asset.underscore
SOL-20 add content type filters instead of extension, fix css issues, add filter text to pagination header
SOL-20 Fixing tests to include filter column
SOL-20 PEP8 fixes
SOL-20 Cleaning up code
Merge branch 'dcikatic/SOL-20-filter-changes' of https://github.com/edx-solutions/edx-platform into dcikatic/SOL-20-filter-changes

Conflicts:
	cms/djangoapps/contentstore/views/assets.py
	cms/envs/common.py
	cms/static/js/collections/asset.js
	cms/static/js/spec/views/assets_spec.js
	cms/static/js/views/assets.js
	cms/static/js/views/paging_header.js