Feature/test performance - pytest speed up

[scottmcdonnell]

Problem
pytest all tests running very slow as all database tables are created and dropped for each test

Solution
move the table creation and drop to once per class setUpClass and tearDownClass.
Set up a Sqlalchemy session in each task setUp that is rolled back in tearDown.

Result: big speed increase in running tests.

[frankrousseau]

Hello @scottmcdonnell,

Thank you for this very helpful contribution. Could you make all tests green? If not we'll have a look at it. It seems most of them are ok.

[scottmcdonnell]

I took this speed up from another project of ours and adjusted it from pytest fixtures to your unit test classes. Unfortunately, I don't have the bandwidth at the moment to debug the few tests that are failing. If you don't get to it I can look at it later this month.