improve topbar

The icons used to show the menu open (`png/hamburger-icon-open.png`)
and closed (`png/hamburger-icon-closed.png`) have been added.

Changed `inc/topbar.default.html` to use the png icons instead
of a svg file.

A new page `nojs-menu.html` has been added for when
JavaScript is disabled.

Changed `bin/gen-top-html.sh` VERSION from to "1.4.4 2024-04-21"
to "1.4.5 2024-04-23".

Sorted top sections in `inc/md2html.cfg` and added
a section for `nojs-menu.md`.

Fixed `ioccc.css` so that the topbar and related pulldown
menus had the correct background colour.

Ran `make www` to perform the above.

TODO: Detect when JavaScript is disabled and display:

		Please
		Enable
	      JavaScript

      As a link to the new `nojs-menu.html` page.

TODO: Fix a problem on wide screens where some of
      the righthand edge pulldown menus are cutoff.

TODO: Fix the 5 HTML 5 errors introduced by the topbar code.

ioccc.css

@@ -480,7 +480,7 @@ a:active {
 
 .topbar {
   width: 100%;
-  background-color: white;
+  background-color: whitesmoke;
   height: 72px;
 }
 
@@ -540,7 +540,7 @@ a:active {
   font-weight: 500;
   color: #154c9f;
   text-align: left;
-  background-color: white;
+  background-color: whitesmoke;
   left: -100%;
 }
 
@@ -751,8 +751,7 @@ a:active {
   top: 20px;
   height: 48px;
   width: 48px;
-  border-color: #154c9f;
-  border-width: 0.5px;
+  border: none;
 }
 
 .hide-content {