Control validation testcase counts

[therealryan]

Some of the validation checks can produce a large number of individual test cases. For example, FlowIdentityCheck makes sure that every flow in a model has a unique identity. It creates a test case for every pair of flows, so the number of test cases grows very quickly as the number of flows increases.

This doesn't seem to be a problem when we run the tests via the commandline, but IDEs will probably be doing a bunch of work (creating widgets, laying out UIs, etc) on a per-test-case basis. Thus you can find that running the validation tests in an IDE is a painful choppy-UI experience on larger models.

It'd be nice to offer a way to package multiple checks into fewer junit test cases.