move isMobile() to support js, as it has no jinja2 in it

internal/js/files_support.js

@@ -628,3 +628,8 @@ function prevPage()
     resetNextPrevButtons()
     return
 }
+
+function isMobile() {
+    try{ document.createEvent("TouchEvent"); return true; }
+    catch(e){ return false; }
+}