Set the repository classloader as the context classloader in the workflow manager

The repository does not set the context class loader to it's own classloader. This leads to problems when the repository is accessed in a non-embedded context.
See e.g. the HST WorkflowPersistenceManagerImpl#getWorkflow method for a contemporary workaround.

Note that the context class loader does need to be set for JDO (this is also in the specification). In cross-(web-)context calls, this needs extra support.