PDE has a wizzard to cleanup a manifest, but this is currently quite
hidden. One can select from the context menu Plugin-Tools>Organize
Manifests, or one can open the manifest editor and under "Exporting" to
open the wizard. Especially the second one indicates tha this is more a
task done before exporting the plugin (what most of the time happens in
a CI build instead from the IDE) and is not accessible when one of the
other tabs are open.

This change adds a new icon at the toolbar next to the run icons so it
is visible on every tab so people hopefully use tthis feature more.