use partitioned ObjectDatabase.getAll() in GeoGigFeatureReader instead single db.get per feature
remove bounds hack in GeogigFeatureReader
split out IniFileConfigDatabaseTest as an abstract test suite for ConfigDatabase implementations
Shrink up the number of databse roundtrips in DiffTreeVisitor.

DiffTreeVisitor was calling ObjectDatabase.get() for each bucket tree.
This patch makes it call ObjectDatabase.getAll() for all the buckets in a tree
instead, reducing considerably the number of db queries.