Re-factor "billing note"

Exchanging `patient_data.genericval2` for `patient_data.billing_note`
throughout the code base.  Also adding some Billing Report, 837, 835,
270, 271, and dated reminders fixes and tweaks.
Promoting discussion of removing the "generic" and "user" fields from
database.sql
Busted this stuff up into several commits.  Unfortunately I did a pull instead of a re-base against master, and don't yet know how to go about correcting it, so the commits will need cherry picking.  The sendmail stuff, when split into a commit, will be accompanied by a global and a configuration list, as well as context instructions for use.  It probably should be in the alerts stuff.  I don't know if that particular giant block of code has gained the ability to send mail or reminders yet.