Refactor to remove much repeated code

	modified:   @LPModel/BuildVectors.m
Add all code necessary to use demand profiles for per-capita demand

1. Calculate population of each zone from each file

2. Allow input of function specifying "demand profiles," which map a
profile numer and a year to a per-capita demand, which is multiplied by
the population to get the actual demand.

	modified:   @LPModel/BuildVectors.m
	modified:   @LPModel/LPModel.m