added indexes on the virtual alias tables

When you're hosting a couple of hundred aliases, you will benefit.
It seems safer to create the index and deal with the slight overhead
for just a couple of records, as opposed to not having these
indexes and deal with serious performance issues if you have
lots of aliases on the machine.

roles/mailserver/templates/mailserver.sql.j2

 	PRIMARY KEY (`id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
+CREATE UNIQUE INDEX name_idx ON virtual_domains (name);
+
 CREATE TABLE IF NOT EXISTS `virtual_users` (
 	`id` int(11) NOT NULL auto_increment,
 	`domain_id` int(11) NOT NULL,
 	FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
+CREATE UNIQUE INDEX email_idx ON virtual_users (email);
+
 CREATE TABLE IF NOT EXISTS `virtual_aliases` (
 	`id` int(11) NOT NULL auto_increment,
 	`domain_id` int(11) NOT NULL,
 	FOREIGN KEY (domain_id) REFERENCES virtual_domains(id) ON DELETE CASCADE
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 
+CREATE INDEX source_idx ON virtual_aliases (source);
+
 {% for virtual_domain in mail_virtual_domains %}
 INSERT INTO {{ mail_mysql_database }}.`virtual_domains` (`id`, `name`)
         VALUES ('{{ virtual_domain.pk_id }}', '{{ virtual_domain.name }}');