The goal is to make the css replacement accessible in other contexts,
for example for the manifest.

squashed a whole bunch of PRs

closes #1907
closes #1908
closes #1909
closes #1910
closes #1911
closes #1912
closes #1913
closes #1914
closes #1915
closes #1916
closes #1917
closes #1918
closes #1919
closes #1920
closes #1921
closes #1922

ran svgo over all the admin svg files to strip all unneeded cruft.

using icons from https://materialdesignicons.com/