Switch from SimpleMDE to EasyMDE (#13333)

Switch from SimpleMDE to EasyMDE (#13333)

* Switch from SimpleMDE to EasyMDE

Signed-off-by: Andrew Thornton <art27@cantab.net>
* use webpack to webpack the easymde css

Signed-off-by: Andrew Thornton <art27@cantab.net>
* move css to only css

Signed-off-by: Andrew Thornton <art27@cantab.net>
* move loading codemirror modes and addons back in to footer.tmpl

Signed-off-by: Andrew Thornton <art27@cantab.net>
* Fix arc-green

Signed-off-by: Andrew Thornton <art27@cantab.net>
* as per @silverwind

* reinstall codemirror

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lauris BH <lauris@nix.lv>