Implement DB management API

[DavidLeoni]

It would probably be useful to have the db record:

• whether or not transitive closure has to be performed
• some extra provenance info at import time.For example: xml filepath origin like /home/david/lmf/wn-test.xml, who imported, when, additional notes

[DavidLeoni]

For the provenance LexicalResource can have associated MetaData class, but that metadata is to state who / how the resource was created (and it is not specified in UBY 0.7 DTD). We need metadata which is more like a db log:

• 12-05-2012, Mr X: Imported /home/david/lmf/wn-3.0.xml

Added lexical resources: Wordnet 3.0 , automatically created, etc <-- here we put LexicaResource MetaData

• 14-06-2012, David: imported ftp://diversicon.org/lmf/dom-test.xml

Added lexical resources: Test Domain 1.0 , automatically created, etc <-- here we put LexicaResource MetaData

TODO: think about logging / describing merges and removals