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.
refactor of redirect after login

user story https://www.pivotaltracker.com/story/show/64997344
refactored store_location method so conditional logic in the
method has a much clearer intent based on code review suggestions