Introduce a new capability via filter for edit_javascript

This will be applied only when the Custom Javascript Editor is
active. We'll account for this role separately at the user level.
Introduce a method for adding the edit_javascript capability to a user
Consolidate super admin and javascript caps into one caps area
Consolidate capabilities update for super admin and standard
Merge pull request #185 from washingtonstateuniversity/prep/custom-javascript

[PR] Introduce an 'edit_javascript' capability required to use Custom Javascript Editor