Improve login code so that it can be included more easily on controllers including being able to maintain referring page URL.


- Migrate from Login to account controller
- Add predispatch suggestion to all controllers
- Move github login to predispatch for those account related controllers that need it
- Pass in referring URL so that we can redirect back to the correct page post login, e.g click on "What are you working on when logged out" and it will redirect you to the edit post page after login. Similarly when on post as a logged out user and you click login, redirect to the post rather than the homepage.
- Add some more security using predispatch on edit post controller so that you cannot view the edit form
- Added redirect helper