Add code dealing with GPS status change.
NullPointerException fix.
Better LocationServiceFusionThread check before push.
Merge branch 'feature/location-status' into develop
Re-enable LEVEL_GPS_ENABLED message.
Add static method for checking whether GPS is enabled or not.
Start to change Sense to singleton pattern.
Minor change to Sense singleton.
Add new init and new method for checking whether a specific service has been enabled.
Merge branch 'feature/sense-singleton' into develop