Merge pull request #215 from pedrolf/master

Upgrades Android plugin version.
Merge pull request #216 from pedrolf/rosactivity_foo

Refactored android_core so RosActivity can be used as a component.
Merge pull request #217 from pedrolf/master

Adds flexibility to NodeMainExecutorService notification.
Merge pull request #218 from pedrolf/master

Draw occupancy grid layer in grayscale instead of three colors.
Merge pull request #219 from pedrolf/master

Gives the user the ability to find out whether the service is being shut...
Fix buffer usage bug.
Merge pull request #220 from SirVer/fix_visualization

Fix buffer usage bug.
Fixes OccupancyGridLayer bug where Bitmaps were being used to draw after
recycled had been called on them.