Fix PageUserAdmin for custom user model.

Don't crash at startup if the custom user model has no first_name and
last_name fields.

The PageUserAdmin still won't actually work, so you'll have to subclass
it and change the fieldsets to include the fields that actually work, but
at least you can import it now.
Modify the custom user model to have fewer fields.

Allows us to test whether PageUserAdmin works or not.
Fix tests throwing another exception during teardown.

This conceals the original error that you actually want to fix.
Test against custom user model to trigger failures.
Remove toolbar for non staff users
Merge commit '2eb9e84' into fix_custom_user_model_admin

Conflicts:
	.travis.yml
order sitemap like the tree structure
display plugin string in alias plugin
Merge branch 'develop' into fix-sitemap
Merge branch 'develop' into alias-fix
Add tests
Change test name
Draft implementation of ExtensionToolbar
Add documentation for ExtensionToolbar
Fix develop.py pyflakes
Merge pull request #3452 from yakky/feature/pyflakes_fix

Fix develop.py pyflakes
Merge branch 'develop' into alias-fix
Merge branch 'develop' into fix-sitemap
Merge pull request #3429 from digi604/alias-fix

display plugin string in alias plugin
Merge pull request #3428 from digi604/fix-sitemap

order sitemap like the tree structure