Add print override for issuing single receipts

Sometimes, you might want to send a personal email and attach a tax receipt PDF instead of sending the PDF with the template email or a particular donor might request a print receipt even though they have an email. You might also want to re-issue a tax receipt that was already sent by email and get a PDF. Currently, you can achieve this by putting the contact email on hold, issuing the receipt to get a PDF, and then unholding the email. Of course, that's a bit of a hassle and you might forget to unhold the email afterwards.

I've added a checkbox on the form to issue or re-issue a single receipt that allows you to override the email and instead get a downloaded PDF. This is only shown when an email would normally be sent.

With regards to re-issuing, the issue method remains set to the value for the original tax receipt. So if the tax receipt was initially sent by email and then a duplicate was generated for PDF download with this checkbox, the issue method remains email (and vice versa).

I also added a fa-ban icon to the Cancel Tax Receipt button, as I noticed it had the default check mark on it.