Removed 'loading.gif'

Removed ‘loading.gif’ in favor of ‘loading’ image already contained in
WordPress.
Changed case of TinyMCE object

Changed case from ‘tinymce’ to ‘tinyMCE’
Cleaned up array notation

Expanded array notation for better readability
Updated 'loading' image URL

Updated URL to use ‘loading’ image already included in WordPress.
Removed 'nopriv' hook

Removed the ‘nopriv’ hook for author change.