composition: Concider the last action as DONE when we get a CAPS or SEGMENT
composition: Keep our GSources in a list making their thread safe
ghostpad: Do not try to be smarter than possible with seqnum

We can have several CAPS event comming at any time and thuse we will
need to rely on elements to handle their seqnum properly as we can not
do a safe guard at our level
composition: Remove DONE fixme
composition: Remove useless functions to add GSources and add debugging
composition: We are now waiting for caps to restart our task
composition: Add an enum to define why we update the stack

Making the code simpler to follow
composition: Avoid emitting COMMITED like crazy
composition: Make sure to remove all updates when updating the stack

The EOS we received before that became meaningless and thus the
associated GSources should no be triggered
composition: add a new failing test for finalize on commit.
composition: Start kindergarten task when going to READY.

And stop it when going back to NULL.

Update tests.