Add a lint indicator that replaces Brackets lint indicator

Removes default Brackets lint status indicator.
Replaces the `errorIndicator` with this `lintIndicator`.

See #61 for more detail on the reasons for this. 
Perhaps the best option here is to keep the magic number (2000) and remove the AnimationUtils dependency. All that AnimationUtils really does for us in this case is removing the class after 2 seconds - which we can do with a simple `setTimeout` anyway.