FEATURE: OTRS link for membership bills
FEATURE: format reference numbers (group to 5 digit groups from right)
FEATURE: RPC interface for admtool
FEATURE: IP ACL (trusted hosts) support for admtool RPC
CHANGE: display 'membership deleted' instead of just id for deleted members
CHANGE: show bill numbers (ids) in more places
CHANGE: refactor email sending to use signals
CHANGE: improved reference numbers in templates
CHANGE: due date at the end of a day (past due date only on the day after due)
CHANGE: No billing for member id 0 (system placeholder member) and don't count member 0 as member
CHANGE: Sort aliases by their names
BUGFIX: only show bills for active members
BUGFIX: handle leap days in billing cycle
BUGFIX: convert to organization must require authentication