Allow bloop to filter out debug output

[jvican]

The sea of logs we get under --debug is difficult to read because it contains too much unrelated information. Particularly, it shows a lot of unnecessary info from Zinc's side, and annoying gigantic classpaths that clutter up our users' screens.

I propose to add a CLI option in CliOptions that is called --debug and takes an optional selector (file-watching, compilation, test, bsp et cetera) so that bloop only shows the debug information related to those tasks. It would be similar to what the reporter does in scalac.

[ioleo]

ScalaSpree - started work.

[jvican]

Fixed in #674, thanks for the hard work @ioleo