Prompt a user if not logged in when voting - Fixes #13

If a 404 is received from the API after posting an up/down vote, show an alert to ask the user to sign-up.
Merge branch 'master' into votes-logged-out-fix

Conflicts:
	lib/assets/javascripts/meducation_front_end.js.map
	lib/assets/javascripts/meducation_front_end.src.coffee
Merge pull request #14 from meducation/votes-logged-out-fix

Prompt a user if not logged in when voting - Fixes #13