amends work done in pull request #6976.

highgui module: mouse wheel - modification keys fixed, wheel event value is CV_EVENT_MOUSEWHEEL or CV_EVENT_MOUSEHWHEEL

highgui module: using event->scroll.delta_{x,y} instead parsing direction and added widget event mask GDK_SMOOTH_SCROLL_MASK for GTK>=3.4

highgui: window_gtk.cpp directive boolean operations or/and replaced by ||/&& to keep compatible with older systems

backport from master

I delete the LIBAVFORMAT_BUILD < 5231 branch, because I couldn't even find FFmpeg with
such a small build number, let alone test with it.

It has already been partially backported by #6199; this commit completes
the backport.

Removed ioctl calls to query for VIDIOC_G_INPUT and VIDIOC_ENUMINPUT since information returned by the calls is never used.
Fixed icvCaptureFromCAM_V4L return value in case of V4L2 camera initialization failure.

(cherry picked from commit 75fcedf0)

(cherry picked from commit c19ed39a)

1. Enabled property retrieval: height, width, FPS
2. Fixed issue when isOpened returns always true even for non-existing devices
3. Ability to work with non-0 device. Camera capture index is taken into account

(cherry picked from commit dbd7912b)

(cherry picked from commit 7825cbeb)

(cherry picked from commit d38fee75)

QSlider does not have getMinimum/Maximum getters. Probably was not
compile tested.

QPushButton was included twice.