Reuse the new infrastructure using Bloop loggers via Slf4jAdapter.

On top of that, in case there's an error in a BSP test case, we report
*all* the logs reported by both the client and the server to help
diagnose problems.

Yay! Goodbye XML.

Which includes build-server-protocol/build-server-protocol#5.

In Windows, the order was different than in Linux and was picking up
`root`, which has no sources and therefore can never compile and output
'Done compiling'.

Read gmethvin/directory-watcher#12 for all the
context.

(including the failed ones).

This is what this commit does:

1. `ResultsCache` no longer stores the successful previous results. Now
it also stores the `Compiler.Result`s, so that a state that has been
compiled allows us to derive summaries and now how the compilation was.
This includes being able to tell the user why a given project was not
compiled (because it was blocked by other ones). This is important to
return a `CompileReport` in bsp-land, but that's implemented in another
PR.

2. The `Result` ADT is moved to backend, `Success` now takes the
reporter too (to check how many error or warnings were outputted to the
user's log), and a reporter is derived from the source infos of previous
Zinc results.

3. The `Result` ADT no longer takes the project as a paramter, instead
we get the project from the `toCompileTask` in `Tasks.scala`.

Frontend is becoming bloated and reporter utils have no specific
dependency in frontend, therefore we're moving them to backend.

BSP clients needed to escape the ansii color codes manually. In order to
avoid this unnecessary work, we default to no ansii color codes for now.
In the future, we will enrich the spec with a flag to toggle ansii color
codes.

See the Scaladoc in `Dag.reduce`. This will allow us to implement
#217 efficiently.