web: version bumps and handle more message body types.

Added handling for text/html, multipart/alternative w/ text/html &
text/plain subparts, and multipart/mixed.

web/index.html

@@ -16,6 +16,9 @@
 .error {
   background-color: red;
 }
+.text_plain {
+  white-space: pre-line;
+}
 </style>
 </head>