Merge 2.4 into master

Original pull requests:

* #2201 from mattip:2.4
* #2235 from alalek:ocl_svm_perf_test
* #2338 from asmorkalov:ocv_gcov
* #2339 from jet47:gpu-warnings
* #2343 from yashdv:template_matching_doc_fix
* #2357 from akarsakov:fix_ipp_compilation_linux
* #2359 from SpecLad:moments-no-vectorize
* #2360 from Evgenij-Gr:XLSreport
* #2361 from alekcac:ios_camera_changes
* #2362 from alekcac:docs_style_change
* #2363 from alekcac:introduction_tut_fix
* #2364 from ilya-lavrenov:unused_field
* #2365 from yashdv:image_tutorial_doc_bug
* #2366 from yashdv:mat_copyto_doc_bug
* #2368 from asmorkalov:ocv_gcc48_warning_fix
* #2370 from ilya-lavrenov:cuda_nlm_typo
* #2371 from ilya-lavrenov:typo
* #2380 from jet47:fix-3562
* #2384 from ilya-lavrenov:perf_match
* #2389 from SpecLad:ios-big-endian