Fixes race condition bugs that can lead to NPEs.
Changes Layer interface to hand in VisualizationView everywhere. This cuts down on the number of parameters to methods like onStart().
Adds new methods to Layer interface to make it easier to preload assets like fonts.
Adds TextShape and PoiShape.
Fixes bug in OccupancyGridLayer. The texture was not unbound after rendering.
Changes XYOrthographicCamera to separate the ROS to screen transform and the camera transform. This was necessary to enable rendering text aligned with the screen.
Merge pull request #186 from damonkohler/master

VisualizationView improvements and bug fixes.