Add an action for retrieving the XSRF-TOKEN

On the first request to the website, we don't hit Rails
since the web server only serves static files. So the Angular app
doesn't get the XSRF-TOKEN, and the user can't sign in.
Check if the user is signed in

We use a dedicated action in access_controller
to check if the there is a valid session among the
browser's cookies.
We GET this action every time the Session service
of the Angular app doesn't know about currentUser.
Don't allow accessing root path while signed in
Fix specs
Use one function for marking menu items as active
Collapse dropdown menu when clicking on a menu item
Add 'Sign in' menu item
Add brand to the menu
Remove toggle button outline
Add classes to the create and repeat links
Add progress bar
Fix spec
Add a rake task for resetting today's repetitions
Get a random repetition in the service instead of the controller
Extract repetition updating logic to the service
Store repetitions inside the service
Decrement consecutive_successful_repetitions in the rake task
Properly handle response 422 when updating repetitions

If the repetition has been run from another device,
trying to run it again causes response 422.
Now no error is shown, and counters are updated.
Show next repetition instantly
Remove obsolete ng-disabled's