TK-8: Refactor the CameraCaptureActivity.
1. Add State to describe which state the activity is now, then we can do things and ignore checking which state is now.
2. Extract the CameraPreview Class, it contain the logic for how to build a more appropriate preivew in current device's screen or for special view.
3. Change the layout for CameraCaptureActivity, make background to show the preivew scene and crop the center view when we captrue picture.
Merge pull request #10 from HunkD/TK-8

TK-8: Refactor the CameraCaptureActivity.