Add scheduled payment mode

[Reidmcc]

Rockfish knows how to make payments, and how to keep track of time; it should have a mode where it makes payments at specified time intervals.

Requirements:

• add non-path (normal) payment functionality and make the mode capable of both path and non-path payments
• the mode should allow payments to more than one account, similar to the [[ASSETS]] list in _examples/samplearbitcycle.cfg
• the mode should have payment interval time keeping independent of TICK_INTERVAL_SECONDS; this will allow payments to have different time criteria. i.e. pay account A with asset W every X seconds, and pay account B with asset Y every Z seconds
• the mode should have its own configuration file and object

[Reidmcc]

After further consideration, this is out-of-scope.