This script is based on https://gist.github.com/lunatic-fox/60e5eb541b299812b3c123fdc0cf4668
by @lunatic-fox

 - Implemented bounding box check using Selenium, since I couldn't find
   a good python implementation. Due to this it's slow, taking about 15
   minutes for the whole `icons/` directory in develop. This check is
   disabled by default and requires the `-b` flag.
 - Improved code organization. Later we might need to split into multiple
   files. Extracted a few more utility functions.

This will need to be moved or merged depending on how we plan to use the
script and organize the `.github/` directory.

This is a much faster implementation than the previous with Selenium.