Add write and delete for rdflibMultiple descriptors

[phil]

Rather than simple assignment this should allow for addition functions

• Assignment with a list of Literal's should be one option, deleting all other values.
• Assignment with an .add() or .append() sytax should also be allowed

[http://openvest.myopenid.com/]

you can now assign a list to any descriptor of types

• rdflibMultiple
• rdflibList
• rdflibContainer (currently assumes RDF:Seq)

set, update and delete work for all these descriptors append will not work as it will append to the returned (cached) list and not to the db triplestore.

This is probably a new crop of descriptors altogether like Stack and Queue with

• append()
• push()
• pop()
• peek()

I should create another ticket for this .... but I'm tired