cxxtest functional separation: unit tests, integration tests, AI tests

[David Hart]

Currently all tests are lumped together, but they should be separated into functional groups such as unit tests, integration tests, and AI tests, where they can be invoked separately, e.g. 'make utest', 'make intest' and 'make aitest', with 'make test' running all tests. Continuous integration (buildbot) will benefit from this separation, where quick utests can be run on every merge, with more complete tests being run periodically and/or on-demand, e.g. triggered by a checkin comment.