Usage of imread(): magic number 0, unchecked result
* docs: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()
* samples, apps: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()
* tests: rewrite 0/1 to IMREAD_GRAYSCALE/IMREAD_COLOR in imread()
* doc/py_tutorials: check imread() result
Correct a mistake in {js,py}_table_of_contents_histograms.markdown (#11260)
* Update py_table_of_contents_histograms.markdown
"Learn to find and draw Contours" => "Learn the basics of histograms"
* Update js_table_of_contents_histograms.markdown
Corrected a seemlingly wronged line of copy in the python documention js_table_of_contents_histograms.markdown
"Learn to find and draw Contours" => "Learn the basics of histograms"