Fixed exceptions, print statements, and long types for gen_pattern.py to be Python 3 compatible (#7994)

* fixed exceptions and print statements to be python 3 compatible; removed long type checks (py3 uses int); whitespace reformatting

* Pulled latest svgfig from upstream

https://github.com/jpivarski/svgfig/commit/f3179a8926508bf0f9021fd4e1f9731c95524a38

Save method should save, instead trying to run inkview

Changed to allow for ISO page size selection, checkerboard pattern now centres itself properly in middle of the page

Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.