Move utility code into a separate module

[Leonard Richardson]

There's a lot of utility code in lazr.restful that is also used by Launchpad and doesn't have anything to do with web services. Files like layers.py, debug.py, utils.py, testing/event.py, and testing/tales.py. They should be moved out into a lazr.util package and the reimport stubs should be removed from launchpad/lazr.

Still in launchpad/lazr are files like xml.py, which aren't big or important enough to justify their own lazr packages. These should also go into lazr.util.