Implement basic TimeDelta and MonthDelta functionality.
Implement basic TimeDelta and MonthDelta functionality.

Move repr() and str() implementation into classes where possible.

LivingLogic/LivingLogic.Javascript.ul4,doerwalter/LivingLogic.Javascript.ul4,LivingLogic/LivingLogic.Javascript.ul4,doerwalter/LivingLogic.Javascript.ul4