Implemented support for isolated side-effects. I.e. application of
side-effects without sending out changes to observing models (though
views are informed - or just non-models in general).

Replay, undo, and redo use isolated side-effects. There are temporarely
non-working - until observers, which provoke side-efects, execute
through a connection meaning these side-effects (forward and backward)
are collected.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>