Fix bug in load_body.
Consolidate types and validators.

All of the symbol enumerations are now kept in Bra::Common::Types, as are their
validation functions.
Move HAML for player variables to variable.haml.

This still needs a bit of cleanup, though.
Test to make sure lists update IDs on deletion.

This test is currently failing.  A subsequent commit will fix this case.
Fix the changing IDs issue.

Objects no longer hold their actual ID, but instead a proc that evaluates
to their current ID.

For HashModelObject parents this proc is just the ID itself, but for
ListModelObject parents it does a search for the object in the current list.
Revamping the Inspector.

The API Inspector now has its own class, which contains all of the state that
the HAML needs in a more convenient manner than as previous.

Much of the API inspector HAML files have been rewritten in parts to make use
of the changed inspector framework.

Also, PlaylistSet and PlayerSet have been replaced with a single class, Set.
Remove PlayerSet and PlaylistSet.