Add route for fetching current user as json

[#31]
Add ember user model

[#31]
Add current user controller

[#31]
Update current user controller's model when logging in / out

[#31]
Add an alias to the current user in the application controller
This way, we can access currentUser anywhere in the app.

[#31]
Show current user information if authenticated and so forth

[#31]
Hide hamburger button when not logged in

[#31]
Dry up logic in sessions controller

[#31]
Add index route, which just redirects to /courses if authenticated

[#31]
Fix hamburger buttons
Remove unnecessary apikey model
It wasn't doing anything, it turns out.

[#31]
WHITESPACE???

[#31]
Make sessions controller transition to whatever our default action is
(as defined in the index route)

[#31]
Add labels to login fields

[#31]
Make sure to clear out users when logging out

Previously, the current user was being cached, so if a user logged out
and a different user logged in, they'd appear to be the first user until
they refreshed the browser. It doesn't look like it's good enough to
just call unloadRecord on the currentUser model (I think it has to do
with the fact that we're tricking Ember Data into thinking that the
current user has an id of `current`).

Let's just unload all users when we logout. I don't think this is so
terrible. We should probably be unloading everything on logout anyway.

[#31]
Merge pull request #33 from gschorkopf/killpack/user_cleanup_alternative

Alternative current user cleanup