JBIDE-17424: Cancel remaining jobs when refreshing

When refreshing, some jobs were still pending and trying to update
UI after it get disposed.
Now, those jobs are cancelled, making feedback faster and avoiding
"widget is disposed" error.
JBIDE-17471 JBIDE-17463 : fix various NPE & disposed widget issues

Signed-off-by: Fred Bricon <fbricon@gmail.com>
JBDS-3050 - An internal error occurred during: 'Computing size'. The profile is currently in use.
JBIDE-17412 : ensure org.jboss.tools.project.examples.projectExamplesXml extension points without urlKey don't break

Signed-off-by: Fred Bricon <fbricon@gmail.com>