FAST Database

We managed to get the scalability-issues out
of the HsqlDB-Dataset and switch back to using
this one as the default.
It scales better to large maps, has better memory-management and offers more features.
A benchmark using 2d-indexing with Z-curves
shows the surprising result that our index
on lat+lon is faster then a z-curve-index.
The TileFileDataSet has memory-management issues
and is currently no longer used.