cupsfilters: Make bannertopdf() work without environment variables

cupsfilters: Make bannertopdf() work without environment variables

bannertopdf() uses CUPS' environment variables to determine the
template file directory, and the printer description (info) and
location entries. To make it easier to use this filter function also
without CUPS, the directory is now supplied as a string pointed at by
the parameters pointer and the printer description and location fields
via the "printer-info" and "printer-location" options or IPP
attributes.

In addition fixed several bugs:

- Free options list correctly
- Free templates file field in banner data structure correctly
- Handle a missing template PDF file correctly, without crash