[Plato] Evaluate Experiments: Approve all values, then save causes exception

[kraxner]

in step evaluate experiments, with a lot of leaves displayed/slow connection/slow server, selecting "Approve all values" and then choosing "save" or "save and proceed" (or possibly other actions) can result in an
org.jboss.weld.context.BusyConversationException WELD-000322 Conversation lock timed out: 2

this is clearly related to #221, "Approve all values" should be blocking the GUI until finished.