Speed up test suite

[vilmibm]

Each one of our tests is currently dropping/recreating the database tables. this is a good most of the time but the test suite is pretty slow.

i did add a TildemushUnitTestCase for use when DB stuff isn't needed; it's in use (and the tests are blazing fast) but there aren't a ton of cases where we can take advantage of it.

this issue is pretty open-ended and might include:

• a test decorator that opts in/out of full database recreation for a given test case
• figuring out how to run tests in parallel
• speeding up our database operations themselves (ie creating the tables once and then issuing DELETE FROM instead of fully dropping and recreating)