Switch MediaModel from sources to sets, close #77.
Add TagSelectView for #78.
Fetch tags and tag_sets with media and connect to query UI for #78.
Add tags to demo view.
Generalize MediaListItemView to ItemView for #78.
Complete TagListView for #78.
Change tag models and views to allow multiple filters for #78.
Add tag selection within a tag set.
Partial implementation of tags for flask routes for #79.
Fix solr tag query, close #79.
Clone tag filter when query copied, close #82.
Load tag filters based on url, close #82.