fixes, meaningful error messages and new features

templates/main.js

@@ -0,0 +1,27 @@
+function contentIFrame() {
+  return document.getElementById("content");
+}
+
+function openNavBtn() {
+  return document.getElementById("openbtn");
+}
+
+function sideNav() {
+  return document.getElementById("sidenav");
+}
+
+function setContent(path) {
+  contentIFrame().attributes.src.value = path;
+}
+
+function openNav() {
+  sideNav().style.width = "250px";
+  contentIFrame().style.marginLeft = "250px";
+  openNavBtn().style.display = "none";
+}
+
+function closeNav() {
+  sideNav().style.width = "0";
+  contentIFrame().style.marginLeft = "0px";
+  openNavBtn().style.display = "inline-block";
+}