redirect users back to most recently viewed page after login

user story https://www.pivotaltracker.com/story/show/64997344
based on recommendations at the devise wiki
https://github.com/plataformatec/devise/wiki/How-To:-Redirect-back-to-current-page-after-sign-in,-sign-out,-sign-up,-update
with slight modifications to request paths that are ignored in the store location method.
I think it would be better to have a array called `BLACKLISTED_URLS` with all the urls which you dont want to store and then check if the url is not in array.