Camera preview example implemented.
https://github.com/adlebzelaznog/colometer/issues/1 finished
Added needed camera releasing methods.
Camera preview is reconnected when coming back to main screen

Screen layout sometimes isn't completely drawed (maybe an emulator issue?)
solved https://github.com/adlebzelaznog/colometer/issues/6
Refactoring: extract all SurfaceHolder.Callback from CameraPreview class.
Refactoring: remove all SurfaceHolder.Callback functionality from the CameraPreview class.
Merge pull request #8 from adlebzelaznog/feature/cameraPreview

Feature/camera preview