login redirection updated

- session_controller redirects to user's links if referrer is root, :back otherwise
- devise initialiser has custom behaviour to redirect to root on privileged routes
- new user_links route added
- tests updated and new test case added on user_flows_test
link to user's links added on index.html.erb
prefer user_signed_in? over current_user in condition
Merge pull request #22 from unepwcmc/link-to-user-links

"go to my links" + new redirection logic