Fix logo being all kinds of fucked on chrome by recovering autoprefixer

Autoprefixer went AWOL during webpack v1 -> v4 (or was it v3 i forgot) upgrade, this MR brings it back (i can't believe chrome doesn't support css-mask and other related stuff without a prefix). Autoprefixer's docs suggest using postcss to load it, even with less/scss/stylus, so I added that, we already use postcss in some library accoring to yarn lockfile and previously it was loaded weirdly in vue build config or something.