make completeness changes trigger when save completes
make completeness changes trigger when save completes

having both set() and save() happen can mean that todos flicker between
being "done" and "not done" as set() triggers and event then a while
later save() triggers another one. Just tick the same todo on and off
a few times.

Note the behaviour might be faster in production but likely we'll have
to fix this anyway.

themystic/justlydone,themystic/justlydone