Redesign the ARMI Migration Scripts

[john-science]

ARMI has some migration scripts from the dawn of time. But after a couple of years of trying, I can't find any examples of these old databases to test and make sure these scripts actually work. (I had to delete a couple that were overtly broken at some point.)

Also, these scripts are fundamentally untestable without example databases to test them on.

For the scripts to remain useful, we need them tested via CI so we can see when they go stale.

My current thinking:

1. Delete the current scripts.
   a. Worry about the future, not the past.
2. Add a new script (if necessary) every time ARMI releases a new, official version.
3. Ensure the scripts are fully unit-tested, or they don't count.

What I haven't figured out yet is:

• The scripts are currently importable in ARMI. Should they be part of the standard import armi namespace? This seems, I guess, convenient. But I've also never seen migration scripts importable as part of a project. They are usually their own directory of helpful tools.