Adds Indicator class
Indicator Class: Implements basic array methods
Can add and remove targets.
Refactors Indicator structure
The Indicator has a single array. Each array object stores a dictionary with a "target" (the actual sprite object being tracked - e.g. hospital, patient) and an "indicator" (the sprite for the indicator). The class manages these arrays and dictionaries when addTarget or removeTarget is called.

This structure allows us to enumerate on a single array and add/remove indicator objects as needed. I was going to have separate arrays for the target objects and the indicator sprites, but that would have been too complex to manage the relationships between the two.

issue #13
Testing single camera instance
Need to implement a single camera instance so we can grab the camera's position from the Indicator class. I need to refactor the camera init a bit to make this happen.

issue #13
Camera is accessed via target instance
Realized we can access the camera via the target's scene, casted to AMBLevelScene. That's what's been done in targetIsOnscreen currently.

issue #13
Implements WIP indicator target follow
Indicator target follow is barebones working. It works when the target is in the top right, just need to tweak the code to make it work in other directions.

issue #13
Fixes indicator positioning bugs
- Indicator calculates correctly under all conditions, including rotation of camera
- Adds padding from the screen edge
- Camera stores world node's rotation for use in calculating indicator positions adjusted for rotation
Indicator: Magic numbers refactoring