Implement patient/hospital indicators

[mctaylorpants]

Design on-screen indicators for active patients and hospitals so the player can find their way around.

http://gamedevelopment.tutsplus.com/tutorials/positioning-on-screen-indicators-to-point-to-off-screen-targets--gamedev-6644

[mctaylorpants]

Create an on-screen indicator class which maintains an array of objects it needs to keep track of. In the update loop, iterate over these objects and:

• Check the target's position and return if it's already on screen.
• Calculate slope to target and determine the indicator's position on screen edge.
• Rotate indicator appropriately.

[mctaylorpants]

TODO:

• Fix the code in AMBIndicator/calculateIndicatorPositionForTarget to correctly calculate coordinates when the target is in all directions. Right now it's really just working in the top right.
• Calculate rotation of the sprite so the arrow points in the right direction always.
• Add some padding around the screen so it's not right at the edge.

[mctaylorpants]

Indicators are complete!