Add base irssi config
Add irssi to dependencies
Add irssi selector to XMonad config

In order to detect it separately from a terminal window, we will need to
ensure the terminal title is explicitly set.
Fix xterm solarized colors

Half of the solarized palette uses the "bold" attribute, which must be
disabled explicitly so that it is rendered with the correct "bright"
color.
Configure irssi for solarized colors
Fix sudo prompt for post-scripts
Add post-install script to install irssi wrapper
Make /quit less easy

Remind me to use Ctrl+A-D, unless I really mean quit.