Revamp for M1

This pulls in work from @sephamorr.

I still want to remove the need for this to exist at all, but until then...

I created an issues type enum, and now you can check a subset of issue types.

I adjusted the whitespace and formatting.

I added a reminder to resign the bundle.

I removed the check for existing signatures, because now that signatures are mandatory on M1, we'll always have existing signatures.

I improved the extra Python check--thanks @sephamorr!

I did some general cleanup.