Design tweaks mostly based on https://www.loomio.org/discussions/3097

Dashboard:
* Lose start new discussion button (discussion [here](https://www.loomio.org/discussions/4412#comment-34196))
* Gentler highlight colour
* Make highlight work on unread lines (with a wicked ! important)
* Groups panel typography & button to bottom
* Nudge live pie to line up with fake pie

Discussion page:
* Better vertical spacing in header
* User-contributed text to black
* Gentler chrome
* Context panel & right-context panel tweaks
* Discussion and proposal headers gentler
* Activity list tweaks, including softening lines, inline names, icons out-dented
* Lose double-quotes around proposals & discussion titles in activity list