Bigmap localization

[zookeeper]

I made a small update to the localization script and noticed that there wasn't a thread for updates and discussion about the bigmap localization process, so I suppose it's time to have one...

The localization process for the bigmaps as of 1.11/1.12 is detailed in the wiki on the MapLocalization page.

EDIT: Updated the script to fix a glitch which caused the innermost pixels of particularly thick black label text to remain very light.

[zookeeper]

Another update: the script no longer requires both black and yellow labels to be present to function, and it'll also produce a clear error message if your labels layer is a layer group which you've forgotten to merge before running the script.