Improve main page (index.html) speed (#1577)

* Inline Font Awesome icons using SVG

* Add license information header

* Preload KaTeX fonts

* Defer loading javascripts

* Cleanup stylesheet links

* Invoke startup script immediately

* Fix typo

* Add leading zeros

website/static/js/index.js

@@ -1,6 +1,6 @@
 /* eslint-disable no-var */
 /* global katex: false */
-window.startup = function() {
+(function() {
     var tex = document.getElementsByClassName("tex");
     Array.prototype.forEach.call(tex, function(el) {
         katex.render(el.getAttribute("data-expr"), el);
@@ -31,4 +31,4 @@ window.startup = function() {
     });
 
     doDemo();
-};
+})();