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

Java inlines static finals if they're defined with a constant expression. In
case of version constants we don't want that to happen, since they obviously
change from version to version. If the user substitutes a different OpenCV
jar without recompiling, we want user code to still have relevant values for
the version constants.

This arranges that by turning constant values into function calls, which no
longer count as a constant expression.

Typo breaks debug build for Android platform.

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

Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.

Common part of all source files is extracted to special header

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 ..)