Set Targets using Calculated Metrics instead of only static values

[#1]

Add the ability to set Targets equal to a Calculated Metric instead of simple static values that currently have to entered by hand for each day (See below).  This would let us set Targets based on prior periods, past results +/- % of growth, etc.  Obviously would make Targets much more flexible, and business effective.

Doing this would largely depend on, or be far more useful when IDEA: Calculated Metrics using eVars made available too.