Features and fixes for nav bar and footer

The updated footer aims to be more useful and better organised, and to avoid duplicating things found on the nav bar.

The nav bar gets dropdown menus (currently for Stats and Media), and a bunch of fixes.

static/static/css/blog.css

@@ -43,9 +43,6 @@ hr {
 ul, ol, dl {
   font-size: 1.1rem;
 }
-.top-bar {
-  height: 50px;
-}
 .top-bar, .top-bar-section { display: inline-block; }
 .top-bar .name h1 a {
   color: rgb(200, 200, 200);