Exclude images and tests from the package data

[RoyalOughtness]

The python package is rather large (relative to limits set by for example Cloudflare Workers) due to the inclusion of among other things, png and test files:

These should be excluded from the package

[alya]

@alexmv Can you take a look at this one, and process/tag it as needed, if you're the right person for that?

[alexmv]

I'm going to tag in @Niloth-p, based on Tim's comment.