Use the KXMLGUIFactory::plugActionList mechanism to populate user-editable menus

Previously we constructed such menus ourselves and were using 'KXMLGUIFactory::refreshActionProperties()'
to load shortcuts for the actions involved. However, due to a limitation
in that method (in 'KXMLGUIClient::reloadXML()', more precisely) the XMLGUI
for Kile was reset to an unmerged state (without the standard actions). By using
'plugActionList' we don't have to resort to 'refreshActionProperties' any more.