RemoteRunner: worker startup scripts

RemoteRunner workers may be given one more scripts to execute on startup by adding an extension method to the worker with the <gtWorkerStartupScript> pragma, e.g.:

The script must be added to each worker class in which it is to be executed, i.e. scripts added to GtRrWorker Object subclass: #GtRrWorker instanceVariableNames: 'uid attributes connectionStrategy resultQueue lastHeartbeat heartbeatProcess heartbeatDelay stopFlag executionContext readProcess exceptionHandlingStrategy' classVariableNames: '' package: 'RemoteRunner-Worker' will not be executed in GtRrInImageWorker GtRrWorker subclass: #GtRrInImageWorker instanceVariableNames: 'remoteRunner connection' classVariableNames: '' package: 'RemoteRunner-Worker' and visa-versa.