Move metatool contentdb package to mt-mods account

[S-S-X]

It is intended to move metatool mod to mt-mods #42

I've already released v1.0.0 package to https://content.minetest.net/packages/-SX-/metatool but there's now also mt-mods account on contentdb. It could be good to transfer metatool there after #42 is done.

There was contentdb update for mt-mods like community projects luanti-org/contentdb#159 and that could be extended a bit, functionality seems to be a bit narrower than what I first hoped for project like account and project wide access for multiple packages.

This could also wait for a while to see if we could get real project/access group support for contentdb as current multi-user/maintainer access implementation is still a bit error prone because it requires a lot of manual work to keep things up to date. It is clearly intended for package specific special use cases but not yet for actual community building.

So multiple maintainer support is new thing, wait a bit and see if it gets better?