Removed the "FileStorage::FORMAT_XML" to generalize format of the String
model.

highgui: Support to change trackbar count in setTrackbarPos and replaced deprecated CreateToolbarEx in Windows.

Signed-off-by: Yan Wang <yan.wang@linux.intel.com>

Signed-off-by: Yan Wang <yan.wang@linux.intel.com>

When accessing global memory by DWORD4, memory bandwidth
can be fully utilized on Intel platform. This patch will
make more image format(e.g. 8UC4) be processed in DWORD4
by work-item. After applying this patch, 3 subcase of
./opencv_perf_core --gtest_filter=OCL_RepeatFixture_Repeat.Repeat/*
can be speedup on HD4000 graphics card with Beignet:
OCL_RepeatFixture_Repeat.Repeat/2, 64% improvement.
OCL_RepeatFixture_Repeat.Repeat/6, 50% improvement.
OCL_RepeatFixture_Repeat.Repeat/8, 56% improvement.
Signed-off-by: Chuanbo Weng <chuanbo.weng@intel.com>

Re-edited the documentation again.

Attempting to re-editing the documentation, to satisfy buildbot error
status.

Edited previous code to change tabs into spaces.

Removed a leading whitespace from a parenthetical comment and corrected the spelling of "maybe"

Added a method "loadFromString" which is based on the "load" one. It
allow to directly pass the XML string which can be usefull and faster
when you have a huge file in a variable.