First steps toward the UUID based API.

You can register nodes by posting a json object to /node, which will
automatically allocate a uuid. This patch probably breaks *everything*
else.
Add a few tests for the new API.

Note that nearly all of the pre-existing tests are failing now; Only
those in tests/unit/api2.py are valid.

Doing this exposed a few bugs, and pointed out that right now we can't
sensibly create Nics/Hnics directly (this arguably doesn't make sense in
general, at least while they must be attached to (head)nodes).
Hnics/Nics have been removed from the list of "public" objects.
Update project_create

...and write some corresponding tests.

Along the way, several issues were discovered, and things were
refactored accordingly. In particular:

* Many things don't need a UUID, so the Model hierarchy changed a bit --
  AnonModel is now called Model, and Model is called UUIDModel. I made
  some guesses as to what should inherit from what, but things will need
  to change, I'm sure.
* _assert_absent and _must_find needed a tweak to their interface, since
  labels no longer exist. This most certainly breaks older code, but
  we'll update that in time.

Old unit tests which obviously correspond to new ones have been deleted.
Update project_delete