Update to modernisation matrix

[Robert Ancell <robert ancell gmail com>]

Work on the modernisation matrix [1] has been going really well,
congratulations to everyone who has been participating!

I've made some small changes to the matrix so we can keep the momentum going:
- I've dropped the trophy goal - no-one was working on it and it's low
priority so I've removed it for now so we can focus on the goals that
are making progress
- I've added lightsoff and quadrapassel to the matrix - these games
are both ported to Vala already so should be easy to work on and this
opens up some new tasks (mallard docs, gtkapplication) that the new
contributors have already learnt the skills for so they can keep
contributing easily.

Keep up the good work :)

[1] https://live.gnome.org/GnomeGames/Modernisation