Merge pull request #3820 from adriaanm/report-filter

refactor error/warning reporting
Restore reporter forwarders in CompilationUnit
eclipse project: repl depends on compiler/lib projects
Cleanup AbstractReporter
Regularize comment hook method

This is currently pretty borken,
but let's at least not clutter innocent
interfaces with this functionality.

Moved `comment` (as `signalParsedDocComment`) next to
the other hook methods in `Global`. For now, it calls
the old `reporter.comment` hook method.

As soon as the IDE is refactored to receive comments properly,
the deprecated `Reporter#comment` method can be removed.
Move more parsing hooks out of reporting.
WIP