Add patron barcode token to staff slips

Purpose/Problem:
Libraries needs vary in regards to hold and transit slips (built already) as well as paging request slips (will be built), and being able to customize these slips with the details relevant to their needs affords more efficiency in their workflows. A comprehensive list of tokens will provide this level of detail.

Description:
At this point in time, the available tokens are minimal and different for hold and transit slips. A comprehensive list of tokens that need to be available for all staff slips is available via this Google doc - https://docs.google.com/spreadsheets/d/1kP3jrlG4jxIAR-hRYCAGId6F875KC_-YZ7svxlRItU0/edit?usp=sharing.