Use Exception::Class for error handling.

* Be able to propagate an error message to the user via either the playerUI or the webUI (javascript?)

Exceptions will be defined as something like this:

package Slim::Utils::Exceptions;

# $Id$

use strict;
use base qw(Exporter);
use Exception::Class::TryCatch;

# Let the callers import these automatically.
our @EXPORT = qw(try catch);

use Exception::Class (

        'Slim::Exceptions::Base' => {
                description => 'An unknown exception in SlimServer has occured.'
        },

        'Slim::Exceptions::Undef' => {
                description => 'An undef value was passed in!'
        },