cmake: introduce setup_vars scripts

* GAPI: Sobel 3x3 with FP32 input

* GAPI: Sobel 3x3 with FP32 input, v2

typo in kmeans doc

* avoid rounding errors

* imgproc: replace condition in matchTemplate

ffmpeg 3.4.2 -> 3.4.5

During the cluster-based detection of circle grids, the detected circle
pattern has to be mapped to 3D-points. When doing this the width (i.e.
more circles) and height (i.e. less circles) of the pattern need to
be identified in image coordinates.

Until now this was done by assuming that the shorter side in image
coordinates (length in pixels) corresponds to the height in 3D.
This assumption does not hold if we look at the pattern from
a perspective where the projection of the width is shorter
than the projection of the height. This in turn lead to misdetections in
although the circle pattern was clearly visible.

Instead count how many circles have been detected along two edges of the
projected quadrangle and use the one with more circles as width and the
one with less as height.