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.
In the code above, `request.path != ` is repeated a lot. So, follow DRY, i think it would be better to use `!ARRAY_OF_URLS.include? request.path`