Unit tests for actuated default in traffic lights

[eugenevinitsky]

• The adding of traffic lights in the grid is not tested; for example, traffic_lights.num_traffic_lights is 0 when called in generator
• need to test that actuation is actually active

[kjang96]

I have some refactoring I want to introduce to the grid that will change the grid interaction hugely. Will push for discussion ASAP.