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.
This is for the case where the user has started a new post and immediate wants to preview it. When clicking "Save and Preview" it creates the post, redirects to the post#edit page with the parameter "preview=true". If the preview parameter is present it automatically opens the new preview window once the page loads - as opposed to saving and then having the user click "Preview" again.