add function to measure battery consumption
write battery levet to a file
Refactored snapshot, it is now a frame grabber. 

I have removed the takePicture thing. I tried also implementing
screenshot, but every screenshot turns black, that is because it is not
possible to take screenshot of SurfaceView (which the Camera uses). 

So the third attempt and current solution uses
setOneShotPreviewCallback(), which I think is neat solution.
Merge branch 'framegrab' of https://github.com/VisualizingSensorInformationOfMobVideo/VisualizingSensorData into framegrab
Little bug, sent snapshot to observers two times
Merge branch 'framegrab' of ssh://github.com/VisualizingSensorInformationOfMobVideo/VisualizingSensorData into framegrab
Merge of framegrab into master
Merge branch 'master' of ssh://github.com/VisualizingSensorInformationOfMobVideo/VisualizingSensorData