Refactor logging

[townxelliot]

Now that we've removed logging almost altogether, we need to come up with a replacement for it (it's too quiet now).

Suggest we have a logger which can toggle between more than two levels of verbosity (was: "lots" or "a ridiculous amount", see #38), so we can cover at least the following (in increasing order of verbosity):

1. User can see that the build is still continuing (e.g. spinner).
2. User can see which step the build is at (e.g. "step 1 of 7").
3. User can see what's happening at the current step and which files are being affected (e.g. "building Java resource file X from directory Y").
4. User can see the commands which are being run (e.g. "running command XXX took N seconds".

We might want to combine or ignore some of these (e.g. do 1, ignore 2, do 3+4).

Architecturally, it might make sense to have a central hub we can publish events to; then add listeners to the hub which log the events (to the console, a file etc.).