Removed some JSHint errors and some resolved TODOs
Removed TODOs aroudn JumpForward/JumpBackward in Playing and Paused states.
Removed some duplicated code, at the cost of an increasingly nested if...
Extracted jump forward/backward decision logic to helper
Reduced complexity by introducing duplication; we've decided that this is more readable.
Stop the media when we complete, so that playFrom will work when re-starting
Corrected emitting of second buffering event when already buffering
Added test aound jumping forward by an offset while not at start (time = 0)