Add support to bool type

Add the bool support to the get function
Added get and set for extra PVAPI property: CV_CAP_PROP_FRAMESTARTTRIGGERMODE
Added PVAPI enums to highgui.hpp
Added "PVAPI_" prefix to FrameStartTriggerMode definition
Added missing comma in enum.
eliminate crash in ipp-accelerated norm and mean functions (thanks to Matt Curfman and Aaron Kunze for the patch)
Update py_image_display.rst
Update py_image_display.rst

OS information removed.
Simplify the code

Simplify the code as @SpecLad suggested.
Change again.

Opps.
Update py_image_display.rst
Merge pull request #2098 from pxli168:patch-1
Merge pull request #2291 from xgvargas:extra-note-for-waitKey
Merge pull request #2144 from nickdademo:pvapi_framestarttriggermode
TAPI: fix OpenCL warpers and test
Fixed compilation error due to missing std::.
TAPI: fix perf test for warpers
some fixes in perf tests
Merge pull request #2325 from alalek:perf_fix
Merge pull request #2376 from GrinIara:master
Fixed typo with indexes in getGradient(x/y) functions.