MINOR: applet: rename applet_runq to applet_active_queue

MINOR: applet: rename applet_runq to applet_active_queue

This is not a real run queue and we're facing ugly bugs because
if this : if a an applet removes another applet from the queue,
typically the next one after itself, the list iterator loops
forever because the list's backup pointer is not valid anymore.
Before creating a run queue, let's rename this list.