Move the typesystem defaults to their own module

Since `TypeSystem` had a nearly 1000 line `__init__` method, I thought it might be nice to move all of that data (and some of the helper classes) to a separate file.

I've only run the unit tests with these changes. It would be a good idea to run this on a couple of real projects since the test coverage is only 50%...
PEP8: file-/module-names should not have underscores. I can change this if you want.