Make edit drills use globals.urls thing
Empty string if song[key] not provided in song

Oops :-p
Moved fc/grid links to nav bar instead
Start refactoring teachables stuff to concerns

Let's start with cards_params
Move more routes to teachables concern
Nuke teachables controller, move to concerns
Get update to kinda work
Fix users signup form
Add (nonfunctioning) search stub on home page
Refactor saving cards/examples so they work
Remove lingering traces of @model_class
Delete difficulty objects when flash card gone
Add delete link in nav on /edit paths
Initially select first card/example in edit page
Shuffle cards semi-sorted by difficulty
Fix ⌘-E/C-E binding in song editor

Apparently, \r is a character, so it would count towards the length in
the match, so the surround would be earlier in the string than wanted.
Styling, remove unnecessary parens.

Because I'm pedantic
Start upgrade of front page: group by mine, newest
Fix everything, add pins

Changes:
* Added pins into teachables concerns
* Made teachables model concerns, added flash cards and user relations
* Fix seeds! Woo!