mapl_tree.py doesn't work

[mathomp4]

@amdasilva asked on OTRS about mapl_tree.py. I thought I'd tried mapl_tree.py long ago (see #775), but I can't find my notes. And when I try to use it, it doesn't work. So, we need to make it work.

Note that I think we might have to remove/add to a lot of the assumptions made in this code. We have directory structures now that never existed in the past. So, we might want flags, etc. that will say "Yes, give me every directory." or "No, just the important ones and stop drilling down if you are at, say, ecbuild"