maintenance:

  - add FS::Misc with send_email subroutine, remove all duplicate code from
    various modules
  - move the realtime_bop from cust_bill to cust_main & change usage slightly.
    invnum is no longer required.  FS::cust_bill::realtime_bop remains as a
    wrapper.
self-service:
  - fix some syntax errors, make payment UI (step one) really should be
    working now