Better standardised and fixes areas of image pasting

Better standardised and fixes areas of image pasting

- Extracted logic to get images from paste/drop event into own file to
align usage in both events for both editors.
- Fixed non-ability to drag+drop into WYSIWYG editor.
- Updated check for table data to look for table specific rich-text
instead of just any text since some the old check was too general and
was preventing some legitimate image paste events.

Tested on Chrome and FireFox on Ubuntu.
Attempted to test on Safari via browserstack but environment was
unreliable and could not access folders to test drag/drop of files.

Relates to #1651 and #1697