[PART 1 of 1] Histogram refactoring

Depends on PR #489

Notable features:
* All histogram collection code is refactored into re-usable functions in common/histogram.h
* Any histogram collection is now being done in parallel (look at histogram_worker)
* SSE intrinsics is used where possible (except histogram_helper_cs_RAW_helper_process_pixel_float - seems to be unused, so i did not bother)

Changes that is needed for future deflicker functionality:
* IOPs can now specify their ROI for histogram
* histogram_helper_cs_RAW_uint16 - histogram of source RAW file, read from mipmap cache)