Now can_edit_site? works, remove can_edit? and its associated tests

- We've replaced it with can_edit_site? which takes a site instead of
  an organisation and uses the same permissions.
Using the new site-org relationship, determine whether a site is user-editable

- The site-org relationship is the new one that gives the ability to
  specify multiple organisations who can edit one (or many) sites.
- Add some tests for this behaviour.
- Fix whitespace in a curly brace block.