move jena deposit models into a shared TDB dataset

same model lifecycle callbacks, no API changes for normal jobs
cleanup jobs now calls destroyModel()
dataset created at <deposits.dir>/jena-tdb-dataset if it doesn't already exist, via spring DI
TDB transactions instead of model transactions

split getModel into getReadOnlyModel and getWritableModel
switched certain jobs to getReadOnlyModel
moved tx management into run() method
removed legacy commit/abort/close methods
modified destroyModel method to obtain a tx if necessary
fixed concurrency problems with XML Transformers and their factories (using prototype beans)
updated some SAXBuilder code to remove deprecation warnings.
Checking for transactions in the dataset instead of tracking in boolean. Updated tests to use new tdb dataset.
Merge pull request #207 from UNC-Libraries/tdb-tx

Moves deposit models into shared TDB store