Merge 2.4 into master

Original pull requests:

* #1283 from melody-rain:new_mog_mog2
* #1300 from kdrobnyh:FilterBilateral
* #1365 from bitwangyaoyao:2.4_bilateral
* #1378 from StevenPuttemans:bugfix_3115
* #1382 from nghiaho12:cascade_classifier
* #1383 from pengx17:2.4_clblas
* #1387 from vpisarev:ipp_imgwarp
* #1388 from bitwangyaoyao:2.4_CLAHE
* #1392 from SpecLad:flann-uninit
* #1396 from melody-rain:2.4_perf_bgfg_cpp
* #1397 from ilya-lavrenov:gitignore
* #1398 from ilya-lavrenov:ocl_perf_gemm
* #1400 from ilya-lavrenov:ocl_test_mog
* #1402 from SpecLad:ocl-samples
* #1404 from ilya-lavrenov:stdcall
* #1406 from SpecLad:gpu-resize-warn
* #1407 from ilya-lavrenov:ocl_test_mog
* #1409 from SpecLad:imgproc-test-memerr
* #1410 from SpecLad:module-samples
* #1412 from jet47:gpu-match-template-nocuda
* #1416 from asmorkalov:doc_hough_circle