Make is_editable_by_user return an instance.

Changed it's name from is_editable_by_user to get_editable_by_user and
also made it return an instance if user is allowed to edit or None
otherwise.
Change call from is_editable_by_user to get_editable_by_user
Merge branch 'development' of github.com:visgence/portcullis into development
Add unittests for get_editable_by_user methods.
Make ajax delete use get_editable_by_user.
Change is_anonymous check to is None.
Handle None and '', and restrict fkey and m2m assignments to editable.
Add styles file for grids.
Move inline styles to grid.css.
Code Refactor
Add a can_view to models.
Update fk's in ajax to use can_view.
Add/update select unit tests.
Modify and add some test fixtures.
Add unittests for can_view. Incomplete.
Add func to create a dialog from a server view.
Add a passwordForm for changing passwords.
Make read_source return both editable and viewable.

Now read_source takes a bool that tells it whether to get editable
objects for a user or just viewable/assignable objects.
Add can_view to model managers.
Code refactor.