Chosen tags

Changed over the Tag field in the editor to be a multiple select Chosen field. The field loads all the tags used within Storytime and allows them to be searched through. 

Added some JS magic to allow for the addition of new tags within that field - type in a tag name, if that tag is not found in the list just press enter and it will be added to the list of options. Create/update the post and any new tags will be created.
What about:
```
attrs = [:title, :draft_content, :draft_version_id, :excerpt, :featured_media_id, :published_at_date, :published_at_time, { :tag_list => [] }]
attrs << :published if publish?
attrs
```
(added curlies around the hash so that the hash is explicit)