Track upstream changes for MDA 0.10

[iay]

The upstream Metadata Aggregator project is making a lot of changes to API and runtime requirements (Java 11) for 0.10.

We should place a maint-0.9 branch in case of any needed development for the MDA 0.9.x series, then start adapting the main branch to the future MDA 0.10 release.

[iay]

Commit 15f1b98 establishes the maintenance branch and gets things moving towards a new upstream release. On the way, I was able to remove a couple of internal classes whose functionality has been upstreamed, and reduce the dependency on the ukf-mda project for the same reasons.

There are some new warnings in the code. I'm not addressing them now because a lot of the remaining code is actually going to end up (or has already been) upstreamed itself. If we're going to delete a lot of that kind of thing, there's no reason to spend time making it pristine here.

Although this is functional, I am going to leave this issue open for future changes, and for the final deletion spree that will happen when we get close to the final upstream 0.10 release.