'METHOD_VAR', 'METHOD_GC' is removed because there aren't equivalent functions
in new OpenCV versions. 'img_right_as_cvMat_rgb', 'img_left_as_cvMat_rgb' and
'depth_map_as_cvMat2' variables is removed because these aren't used.
cvarrToMat() is added because it is compatible with all versions of Opencv
and using the class Mat constructor is eliminated, because is deprecated
in 3.X versions. The use 'using namespace cv' because is called some
functions many times. This keeps compatibility with 2.4.
https://bugzilla.gnome.org/show_bug.cgi?id=760473
Remove calls to gst_pad_has_current_caps() which then go on to call
gst_pad_get_current_caps() as the caps can go to NULL in between. Instead just
use gst_pad_get_current_caps() and check for NULL.
https://bugzilla.gnome.org/show_bug.cgi?id=759539
The opencv element includes were full of duplicates and uneeded headers.
For example a few elements that stopped using gstcvopencvutils still
included that header file.
