* Add theme uploader component
* Add theme to theme browser on upload complete
* Add a minimum height to dropzone area
* Use Muriel style Spinner during upload
* Add file field uploader to dropzone for accessibility
* Delete transient on theme install or theme switch
* Add theme upload REST api controller
* Add theme data to theme controller response
* Add tests for themes api
* Change user cap check to upload_themes
* Add test for users without theme capabilities