Refer to text label related URLs explicitly in own statement

This is part of an effort to make the URL configuration and the control
package more readable and maintainable. I double checked, that all
catmaid.control namespace imports removed, where not in use in other
places.

This commit relates to issue #570.
Remove circles namespace import into catmaid.control

This is part of an effort to make the URL configuration and the control
package more readable and maintainable. I double checked, that all
catmaid.control namespace imports removed, where not in use in other
places.

This commit relates to issue #570.
Fix ORM related bug in annotation creating migration (0019)

The ORM of South wasn't available in all methods needing it. This commit
fixes this. Furthermore, the auth.User model of South's ORM couldn't be
used for the tracing setup.  Therefore, Django's regular User model is
used now.