Add logger for debugging

[natario1]

This tool might be helpful for debugging issues.

Can be controlled with CameraLogger.setLogLevel(). By default will show only errors, so no floods to your logcat.

[codecov]

Codecov Report

Merging #25 into master will increase coverage by 0.7%.
The diff coverage is 44.8%.

Impacted Files	Coverage Δ
...ain/java/com/otaliastudios/cameraview/Camera2.java	0% <ø> (ø)	⬆️
...ain/java/com/otaliastudios/cameraview/Camera1.java	0% <0%> (ø)	⬆️
.../java/com/otaliastudios/cameraview/CameraView.java	33.6% <27%> (-1.4%)	⬇️
.../otaliastudios/cameraview/ScrollGestureLayout.java	26.4% <40%> (+2.3%)	⬆️
...ils/com/otaliastudios/cameraview/CameraLogger.java	91.4% <91.4%> (ø)