Changed desktop notifications to support Firefox.

Pretty much everything of the notification handling was redone.
This is tested on Chromium version '32.0.1700.107 (248368)' and
Firefox version 29 and 27 under linux. More testing would be nice.
Add support for server presets.

To make it even easier for non-technical people to get started with IRC,
this change adds support for presets defined in config.js.  In such a
deployment, instead of requiring users to type in all the server
configuration parameters, subway automatically connects to the preset
server and joins a predefined set of channels.  After that, users may
join and leave channels as normal, but they cannot connect to other
servers.