Alphabetize model lists
# What does this PR do?

The model lists have grown a bit and so, like the doc navbar, I think we'll find our way better by alphabetizing them.
Adding new models will be easy in the README since Markdwon supports enumerated lists with 1. for all items. RestructuredText is more annoying but I'll make one script generate the proper part of index.rst automatically to make sure it's in sync with the README while I'm procrastinating something more important.