The former icon used fill="context-fill", which I believe doesn't work
except in Mozilla's own extensions. So I changed that one to
fill="black" and made a new one with fill="white".
https://bugs.torproject.org/31170#comment:8
I chose these icons for the "on" and "off" icons:
toolbar_icon_purple.svg → toolbar-on.svg
toolbar_icon_grey.svg → toolbar-off.svg
I then made toolbar-running.svg by copying toolbar-off.svg and changing
the stroke and fill from #4A4A4F to #40E0D0.
This one was missing from the redesigned icons. I made it by making a
copy of status-on.svg and changing the fill from #8000D7 to #40E0D0.
I didn't make a separate dark-mode version of the icon.
