Switched user authentication to devise.

Removed sessions controller (not being used anyway) and links updated.
Update tests for devise work.
Merge branch 'devise' into 0.5.3-maint

* devise:
  Update tests for devise work.
  Switched user authentication to devise.
Link the workflow model to the user model properly.

The column is in the model but the relationship wasn't made explicit in the
class.
Tidy up user code and allow editing of profiles.

Users can now edit their profiles (just their name right now) by clicking on
their name in the top-right corner.

Also a bit of tidying up of CSS, forms, etc.
Merge branch '0.5.3-maint'

* 0.5.3-maint:
  Tidy up user code and allow editing of profiles.
  Link the workflow model to the user model properly.
  Update tests for devise work.
  Switched user authentication to devise.