Return to the previous page that the user was on upon logging in

[sbrl]

If I click login while on a page called 'Oranges' for example, when the login process is completed I end up on the main page. This is really annoying as I lose my place on the site and forget what I was doing.

We should redirect the user to the exact page that they were upon before logging in.

This is already partially implemented, but currently has some bugs. We should finish the job and fix all the bugs.