Update and clarify the task naming system

[mds1]

From #55 (comment)

The PR calls this upgrade 4 but this file is called 2-*, which feels confusing. Should those match at all? Or are the 0/1/2 number prefixes for existing task folder names just communicating the order they were added to the repo for some reason?

They are meant to indicate the order in which they are executed, not map to the upgrade numbering.
There have been several upgrades which did not involve contracts, so they aren't reflected here.
We should clarify/improve on this system when we get a chance.

[mds1]

We now have a consistent naming and numbering convention, so closing this as completed