New version of Java wrappers' generator uses different wrappers for VideoCapture
on Android and desktop to prevent binary compatibility issues.

- enable auto-wrap of VideoCapture;
- minor refactoring of generated code templates.

Introduced new Java API
void org.opencv.core.Core.setErrorVerbosity(boolean verbose)
used to suppress output to stderr from OpenCV's asserts

Common part of all source files is extracted to special header

This fixes random failures in Java wrappers.

Based on pull request #31 (thanks to Eric Christiansen)
Support for Java is turned off by default and can be enabled setting
BUILD_opencv_java to ON (e.g. cmake -DBUILD_opencv_java=ON ..)

fixing bug #1987(android keeps RGBA in alpha pre-multiplied form, Mat <-> Bitmap should handle this correctly)