new comment design

-   all (sub)comments are visible by default
-   the show_comments button is obsolete
-   the new_comment button gets the same arrow as
    showhide_buttons
-   lines on the left make it simpler to understand the
    tree structure
-   the metadata is reordered
-   new comment forms don't have their own heading
refactor comment design with robin
slightly lighten fg1 color
white background in all overlays
minor css changes

some tweaks I needed for implementing the new grüne nrw theme.

most importantly I gave the badge background image a white
background and added an html element wrapping the subnav and
search.