Fix sparse index filters method signatures
Add the zero-chunk filter
Cleanup configuration files
Refactor the garbage collector.

The GarbageCollector is now an abstract class for which alternative
implementations can be implemented.
Two proposed implementations are a NoneGarbageCollector that does
no garbage collection. This is interessing for research, testing, and
usages where no garbage collection is necessary.
Also a mark&sweep GC would be interessing.