Ensure that the machine weighting predictor is always trained before requesting a model run (it wasn't happening when using gold standard occurrences)
Improve log message
Combine ModelRunRequesterException and MachineWeightingPredictorException into one ModelRunWorkflowException class. This is caught at the top level of relevant public site and Data Manager routines.
Also remove @Transactional from AdminDiseaseGroupController.requestModelRun, so that the transaction has a chance to roll back before the ModelRunWorkflowException is caught.
Fix test
Merge pull request #276 from SEEG-Oxford/various-fixes

Various fixes