* imgproc: fix bit-exact GaussianBlur() / sepFilter2D()

- avoid kernels with bad approximation
- GaussiabBlur - apply error-diffusion approximation for kernel (8-bit fraction)

* java(test): update features2d ref data

* test: update test_facedetect

- disabled xfeature2d dependency for java wrappers
- fixed java wrappers build after cmake rerun
- disabled opencv_ml tests temporarily
- fixed Imgproc usage in java tests

Java API: fixed problems in video and ml modules; generated test stubs for all exported functions (now we have 1701 tests).