Intermediate commit on a new datastore API. Already added some scanning
functionality to the mongodb store. Tests are still required. The new
datastore API is not yet used.

Created a custom global event listener for memory management.
Tried to implement and test as much data store features for in-memory,
mongodb, and hbase as possible. There are still lots of problems:

HBase and Mongodb scans do not recognize writes after scan start, even
without any read caching. Hbase shoulb be able to do otherwiese but does
not.

TODO: One should be able to activate scanning for read-only models.
Cache and BulkInser sizes need to be configurable.

Mongodb does not support bulks upserts. There is not
IBulkInsertExtension possible.

Mongodb's key handling due to non lexicographical ordering of byte[]
does not work with the db tests, but works for EMF-Frag (only keys that
can be filled are used).
Organized imports. Configurable scan and bulkinsert sizes.