connectedComponents and connectedComponentsWithStats in
imgproc accept 8-bit single channel image only for input.

- added new functions from core module: split, merge, add, sub, mul, div, ...
- added function replacement mechanism
- added example of HAL replacement library

See https://github.com/Itseez/opencv/issues/5721

COMMENTS:
* The second __syncthreads() is necessary, I am sure of that.
* The code works without the first __syncthreads() too, but I have however added it for symmetry. Anyway it doesn't affect time performances, I have checked it with some profiling with nvvp

In oder to guarantee SIMDness between the two compilation steps we choose the
highest SIMD size that is optimized in the kernel for the first step.

wsfixed