Add Do Not SMS communication preference option

currently we have Do Not Phone, Mail, Email, and Trade... but what about SMS? This is a very common method of communication and I think the option should be included in core rather tan making people create a custom field to handle this - which does not display alongside the other communication preferences without template hacks.

Attached is a patch that should add the support for this. I wrote this patch against the 2.2.5 release. The only think I haven't included is the ALTER TABLE statement for the update script since I wasn't sure where this should go. The SQL for that would be:

ALTER TABLE `civicrm_contact`
ADD `do_not_sms` tinyint(4) default '0' AFTER `do_not_trade`;

And civicrm_cache needs to be cleared, but I assume that happens on an upgrade automatically (took me a while to figure out while my changes hadn't taken effect!)