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