Remove dependency on Sass

- Convert *.sass files to vanilla CSS
- Start using CSS variables
- Add PHP minifier

libs/minify/data/js/keywords_before.txt

@@ -0,0 +1,26 @@
+do
+in
+let
+new
+var
+case
+else
+enum
+void
+with
+class
+const
+yield
+delete
+export
+import
+public
+static
+typeof
+extends
+package
+private
+function
+protected
+implements
+instanceof