`kgx` used to link to a private shared library installed under
`/usr/lib/$ARCH/kgx`, and as a consequence needed a custom RPATH to be
set. This library has been dropped recently, so the custom RPATH isn't
needed anymore.

NEWS generated by appstreamcli, hopefully keeps things happy

This made sense once, but not anymore

Fix: #109

Thus rather than observing page lifeycle, we were keeping them alive

We were leaking multiple refs via GTask and unneeded strong refs

Additionally if the object were to die (or be removed from UI) we could
hit a race when :command is slow to spawn, or if it's death is out of
sync with ours. By using an explict weak pointer we can check if `self`
has been nulled out and thus abort.

Fix: #102