#20 Remove depenency on exist jars.

[Geoff Drake]

The ContractRepository interface currently returns the contact as a xmldb resource. This means we need the exist jars (several of them) in the AgentWS project.

I propose we change the interface to return the contract as a String containing the xml. This would remove the need for the exist jars.

It should be done in two steps:

1) Introduce a new method to get the contract as a string and deprecate the old method.

2) Once the Observer, Analyser, ContractStorer Agent etc. have converted to the new method remove the old method and jars.