Merge pull request #526 from ControlSystemStudio/sns4

Sns4
o.c.apputil.ui.ImageTabFolder: Dialog was partially visible on Linux

When taking CSS window or complete screenshot, on Linux this included a
blank area where the dialog used to be
Merge pull request #529 from ControlSystemStudio/bug515

o.c.apputil.ui.ImageTabFolder: Dialog was partially visible on Linux
o.c.simplepv.pvmanager: Access PVManager Activator

When org.csstudio.utility.pvmanager contained the PVManager classes,
this was not necessary. Since they're extracted, and
cs-studio-thrirdparty has a org.csstudio.utility.pvmanager plugins that
only re-exports org.epics.pvmanager, access to the PVManager classes
would no longer activate rhe org.csstudio.utility.pvmanager plugin, and
thus the PVmanager was not initialized.