Add fixtures and improve tests

[cdubz]

Tests are a bit weak right now, fixtures will likely help to write more specific and useful tests in a lot of situations (instead of relying the fake data generation).

Tangentially related, the fake command could be refactored to generate more realistic data - right now entries with duration intersect and make little sense (e.g. feedings while baby is asleep).

[cdubz]

5dec231 greatly improves the quality (and speed!) of the fake command. This should improve some testing on its own, but will also help to create better test fixtures.

[cdubz]

Oops. Need to re-add the random color choice when Diaper Chabge is “solid” in _add_diaperchabge_entry

[cdubz]

Random solid colors fixed in 4aa51e4. On to fixtures...

[cdubz]

452ce19 adds Dashboard card tests using fixtures.