Make confirmed signup ids available in order comments, view order pane and order confirmation mails

There was a suggestion at #783994: Displaying Signup Date on Order/Invoice to include the date of the event in the order as well as the sid.

Changing title to account for scope of this patch.

We save the sids in the admin comments so that they're archived if they're deleted, make them visible in an order pane so admins and customers can see them easily, and make them available as an order-signups token ($order_signups) in the template so that we can include them in the order invoice mail.

The text that accompanies the sids is themable.

The motivation here is that the sid is a fast way to confirm that a customer is signed up for a specific event.

This is committed, with an extra line break removed and some function headers added:

http://drupalcode.org/project/uc_signup.git/commit/cc89726
http://drupalcode.org/project/uc_signup.git/commit/8c89c7a

Hi Ezra,

I got to this issue from #783994: Displaying Signup Date on Order/Invoice as I am looking to display the date of an event on the ubercart invoice. I have tried adding $order_signups to an overridden uc-customer.tpl.php file but nothing printed. I'm probably being dim as under deadline pressure, is $order_signups for the ubercart invoice or for signups confirmation email?

It also says "We save the sids in the admin comments so that they're archived if they're deleted, make them visible in an order pane so admins and customers can see them easily" but I dont see anything in either comments.