Access org.csstudio.utility.pvmanager to force start

Partial fix for #527: When BOY accesses the PVManager, it does that by first accessing one class in the org.csstudio.utility.pvmanager plugin, so it's started, it initializes the data sources, all is fine.

The org.csstudio.utility.pvmanager plugin thus doesn't need to be force-started by the product, and consequently it's again possible to select the workspace on product startup.

Other plugins (probe, …) still try to use org.epics.pvmanager.* directly, not triggering the org.csstudio.utility.pvmanager plugin, so this doesn't fix the PVManager completely.