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
further refactor of redirect after login based on code review

user story https://www.pivotaltracker.com/story/show/64997344
tidied up matching line based on suggestion by @yarospace
refactored black_list method reduced to single method and used
rails route helpers to prevent hardcoding paths based on
comments by @yarospace and @yggie.
Addition of controller and view specs
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
Merge pull request #498 from PurityControl/user_redirect

redirect users back to most recently viewed page after login