Merge 2.4 into master

Original pull requests:

* #2407 from codyrigney92:LKOptFlow_NEON
* #2429 from ilya-lavrenov:master_compatible_tests
* #2432 from ilya-lavrenov:summary_py
* #2439 from ilya-lavrenov:typo
* #2443 from waveform80:issue-3554
* #2445 from ilya-lavrenov:ocl_perf
* #2448 from akarsakov:ocl_cxt_termination
* #2457 from ilya-lavrenov:ocl_calc_hist

(all the OpenCL stuff skipped)