Cannot get working in chrome reliably due to conflicting handling of
events and drag+drop API. Getting attachment drop working breaks other
parts of TinyMCE.
Implementing current work as should still work for MD editor and within
FireFox.
Related to #1460
Currently fighting between sortable and tinymce mechanisms which prevent
this working due to the different events stopping the drop event while
needing the dragover for cursor placement.
- Created new dropzone component.
- Added standard component event system using custom DOM events.
- Added tabs component.
- Added ajax-delete-row component.
