CONTENTBOX-75: Tagification of Widgets

Extensive updates/changes/additions/etc. to support inserting "tag"
based widgets in CKEditor. Also includes some extra definition data for
widgets (icon & category), as well as some UI changes to widget list
view and "insert" view for CKEditor.

The "234" files is a bit deceiving. Most of them are images :)

Please let me know if you see any issues, and I'll do my best to get them knocked out. Thanks!