fix #11368: adjust event dispatch

The crash on deleting ROIs then saving was intermittent, so do a bunch of them to make sure that Insight doesn't crash and that they really are deleted and don't come back from the server.

Also, this code touches the tree viewer, so also keep an eye on the project tree and do things with it and affecting it to make sure there are no regressions in how it responds.

Fixes http://trac.openmicroscopy.org.uk/ome/ticket/11368.