Extend @Transactional support to take advantage of read-only

[nealeu]

trafficstars

We want to be able to do something like:

@Autowired
private DataOperations dataOps;

@Transactional(readonly=true)
public void getSomeData(Model model) {
    ResultSet results = dataOps.query( resultClass, searchSpec, numResults );

    // Stick the results in the model
}

For the simple case (for now), we can autowire a single authoritative Store instance. In future well need to pick a Store instance on the basis of wether we are reading or writing (read only can use nonAuth).