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.
I tried adding the curlies and it seemed to work. All tests continued to pass and manual testing seemed to work.

```ruby
def permitted_attributes
      attrs = [:title, :draft_content, :draft_version_id, :excerpt, :featured_media_id, :published_at_date, :published_at_time, {:tag_list => []}]
      attrs << :published if publish?
      attrs
    end
```