Added image-manipulations android sample, other samples are updated; added Mat.size method to java API.

Removed some debugging insertions.
Added test for face detector.
Allowed tests to write on sdcard.

java tests: Mat.inv and Mat.cross implemented, almost all Mat tests finished except put, get and dispose

More code review feedbacks addressed: Mat c-tor and setTo uses Scalar, Java Mat::dispose() calls C++ Mat::release().