It should now be possible to fully export our symbolic icons from a
single central file.
My long-standing bug of librsvg#250 is still opened and unfixed, but it
turns out most issues I encountered are anyway also problems when
recoloring symbolic icons in GTK+ (like using strokes instead of
fills!). So let's just bypass all problems at once by accounting for
these issues in the design.

(cherry picked from commit 4c68d5df)