Add Tags

* Add tags to API
* Add tags to Outpost
* Add tag association
* Replace issues form fields with tags
* Add specs for new stuff
Fix column type; add tags to articles
Add tags to Articles API [wip]
Add tags facet to index
Schema update
Add tags to article API
Add test for API tag filtering
API v3 version bump
Merge remote-tracking branch 'origin/master' into add-tags

Conflicts:
	db/schema.rb
Add Tag permission
Switch back to issues form fields for now
Migration update
Add Description, is_featured bool to Tags
Add form field override for tags
add reverse-association for taggings
Schema update
Migration update
Add Tag permission for all Issue permission users
Merge remote-tracking branch 'origin/master' into add-tags
Reference meta file for Tags