Preferred language and patron receipts

[Garry Collum]

Currently the preferred language in a patron record only works with action triggers, which is a excellent feature that we have just started using.

A nice addition to this functionality would be to extend it to print templates, so that we could have cko receipts, bills, etc. in the patron's preferred language.

This could be done either by using an alternative template method as used by the triggers, or possibly just by making the variable visible to certain print templates.