Show page thumbnails in pages list (#221)

* convert pages / pageentry to ts
* render page icon
* adjust for smaller screen
* show favicon even if thumbnail exists

assets/main.scss

@@ -134,3 +134,16 @@ a:focus {
   box-sizing: border-box;
   overflow: hidden;
 }
+
+// Make available to screen readers while hiding element visually:
+.sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0, 0, 0, 0);
+  white-space: nowrap;
+  border-width: 0;
+}