unit test and minor fixes to tracked-controls

[ngokevin]

Description:

Was looking at a controls bug and wanted to sweep up to add coverage.

Changes proposed:

• Full unit tests, docstrings, comments.
• Make previous unit tests more clear on what they're testing. Before the test names were a glob of numbers.
• Move .update() to .updateGamepad() method. Don't need .update() handler since .updateGamepad() is called every tick. Also to not call handlers from other handlers.
• Better handle initial states. Ensure that events aren't fired on the initial tick if it doesn't make sense to. It seemed many events were being fired due to uninitialized states.
• Make .handle*() methods more consistent by having them all return a boolean.
• Make .handleAxes() not take an argument since it's a method and has access to component members
• Rename this.previousAxis to this.axis since it represents current axis and is not used for any delta calculations.
• Set initial button states so we don't have to do previousButtonState = buttonStates[id] = buttonStates[id] || {}