B-Tree Event Store

This is a replacement for the in-memory event store of JEPC core. The B-tree event store persists every event stream in its own B-tree on disk. It takes advantage of the posibility to insert bulks into an B-tree very fast and is so able to write significant more events per second than an EP provider can process. Therefore, the B-tree event store will not become a bottleneck in JEPC applications.