Replace deprecated CRM_Core_BAO_Settings functions

Created by: demeritcowboy

Alternate PR to address issue https://github.com/jake-mw/CDNTaxReceipts/issues/74

There's a pending separate fix from @KarinG for receipt_serial so I'll rebase this after.

This is basically the same as PR #97 but with most of the comments there applied. It's more or less what I was testing with while testing 97, and I did another round of testing here.

I also faked an upgrade to test out the one that was marked "unsure" and it updates the right db field and everything seemed ok. Longer term the base upgrader file should be updated to match newer civix's.

Also two of the lines being updated had tabs (!!) instead of spaces so fixed that while at it. TABS!!!!