BS4 by default, BS5 optional

Bootstrap 4 w/ jQuery is used by default unless bs5 is enabled in
settings/ui. bs4 also now has a jellyfin-style look.

scss/bs5/compile.sh

@@ -0,0 +1,10 @@
+#!/bin/bash
+css_file=$(echo $1 | sed 's/scss/css/g')
+min_file=$(echo $1 | sed 's/scss/min.css/g')
+sassc -t expanded -p 6 $1 $css_file
+echo "Compiled."
+postcss $css_file --replace --use autoprefixer
+echo "Prefixed."
+echo "Written to $css_file."
+cleancss --level 1 --format breakWith=lf --source-map --source-map-inline-sources --output $min_file $css_file
+echo "Minified version written to $min_file."