better and more controllable user feedback

[mor1]

again, on a poorly performing network, very little feedback on progress (even with
--verbose --debug, package installation would frequently stall at
"git remote set-url ...", often for minutes), i found myself assuming
yet another network issue had occurred and killing the process, which
probably didn't help leave things in a consistent state.

more
fine-grained levels feedback would also be nice (eg., i often want to
see that packages are downloading ok but i don't usually need to see
all the build output).

[AltGr]

We'll probably separate download from build (and maybe from install) at some point, which would make things more robust and improve parallelism. As that will imply reworking the display of these steps, I won't be improving it much in the current state.