Adding 'Cancel' option on Login Page

Currently there is no way to exit the Login page except by Login in or pressing back in the browser. It is desirable to have a "back" link in there for the users.

This pull request adds a link and config to this purpose.


* Allows a user to exit the login page without having to press 'back' in the browser.
* The configuration entry allows the developer to set the path the user will be redirected to. By default this path will be the same as the 'onLoginGoTo' path
* Documentation updated

If you want any additional change/fix please let me know