Closes #ISSUE

Adds a default sort when no filter query is provided in the keymap
editor.

The default sorting algorithm sorts by the source of the binding
(roughly in order of precedence)
 
- User
- Vim
- Base
- Default
- None (unbound actions) 

within each source it sorts by action name alphabetically.

Release Notes:

- N/A *or* Added/Fixed/Improved ...