Bugfix: insert id-based match at HEAD, not TAIL.

Bugfix: insert id-based match at HEAD, not TAIL.

Before this commit, placeholder windows had any matches that were
defined in the JSON file, _followed_ by an i3-internal match that
ensures the placeholder X11 window gets swallowed into the placeholder
i3 container.

The problem was that the first successful match was deleted, and if
users specified a criterion (title=IPython) that matched the placeholder
window itself (name=IPython), then that match is deleted and the
i3-internal match is kept. This results in the actual window the user
wants to match not being swallowed, and the placeholder window not
displaying any criteria.

fixes #1526