fix issue #5639: Delete all watch expressions
moved DeleteAllWatches menu item push in js/watchPanel.js
Merge remote-tracking branch 'upstream/master' into issue5639
some code improvements
I have included your remarks.
The separator between "Delete All Watches" and "Refresh" is automatically added when clicking on an empty space.
I made yet one more little improvement in eb7fe8d, which causes the option only to be shown when there are actually some watch expressions defined.