Add slack dark theme

add_slack_darktheme.js

// thanks to @laCour for this code snippit in the comment https://github.com/laCour/slack-night-mode/issues/73#issuecomment-287467332
//
// with this theme you'd just append the following to app.asar.unpacked/src/static/ssb-interop.js
// I then use the sidebar theme "Green Lantern" from https://slackthemes.net/#/green_lantern
// #171717,#404245,#424242,#ECF0F1,#4A4A4A,#FAFAFA,#2ECC71,#00A362

document.addEventListener('DOMContentLoaded', function() {
 $.ajax({
   url: 'https://gist.githubusercontent.com/kevcoxe/7b3a872685dbab5229269bfa9f80db3b/raw/5fe9f4bab32382e1ee81d8e82b5b18d2d102d3d4/black.css',
   success: function(css) {
     $("<style></style>").appendTo('head').html(css);
   }
 });
});