Tag form field implemented with tokenfield

test for tags with spaces fails
Updated functional test to use the new tokenfield for tags
Allow for spaces in tags
Removed tag-slugs from everywhere, tags only use their name
Implemented tokenfield widget for tags

Tags are now render as a bootstrap-tokenfield
form widget. They are always split at commas,
commas can never be escaped.
We also use a custom Tag model now for which
we need to do a migration.

Merge branch 'tag-tokenfield'