BUG/MAJOR: applet: use a separate run queue to maintain list integrity

BUG/MAJOR: applet: use a separate run queue to maintain list integrity

If an applet wakes up and causes the next one to sleep, the active list
is corrupted and cannot be scanned anymore, as the process then loops
over the next element.

In order to avoid this problem, we move the active applet list to a run
queue and reinit the active list. Only the first element of this queue
is checked, and if the element is not removed, it is removed and requeued
into the active list.

Since we're using a distinct list, if an applet wants to requeue another
applet into the active list, it properly gets added to the active list
and not to the run queue.

This stops the infinite loop issue that could be caused with Lua applets,
and in any future configuration where two applets could be attached
together.