Rename persistitadapter dir

Mostly automated refactoring:
* Rename the qp.persistitadapter directory to qp.storeadapter to make it clearer that it has both Persistit and generic storeadapter stuff. The former could go into another package, but that it's essential, since the class names are pretty clear.
* Gut ValueRowDataCreator to no longer be generic in ValueSource now that we don't have any alternative type systems. The expectation is that it will shortly become generic in RowData, with an adjusted interface. And that'll be easier without the noise of types generics.