dispatch subgraphs of work to Bloop instead of every module

[propensive]

Fury manages all dependencies between modules, and dispatches independent compilation requests to Bloop, one for every module. Bloop has no awareness of the dependencies between modules.

But Bloop configuration files could be made aware of dependencies between library, plugin and compiler modules (but not application modules), and Fury could take advantage of faster pipelining in Bloop between these modules.

We need to work at the "subgraph" level because it's not possible to get Bloop to run an application in the middle of a build (only at the end), and we can't pipeline compilation across an application module anyway (because it has to complete compilation and run before the next module can start compiling). So Fury will need to compute subgraphs containing at most one application module.

This also requires using BSP to get progress information from Bloop, i.e. the details of when each module starts or finishes compiling.

[propensive]

@tpasternak Your next PR should fix this. :)