Add go version of helper tool

Signed-off-by: Lukas Bachschwell <lukas@lbsfilm.at>

tools/prepare_static_ui_sources.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 
+# script is kept for legacy reasons, please use go version instead!
+
 from jsmin import jsmin as jsminify
 try:
     from htmlmin import minify as htmlminify