adds a helper function to determine year indicies given a starting month and ending month
significantly sped up fac query. sort of getting the hang of this...
nFacsInRange isn't actually a query, its an aggregation, which belongs in the curves namespace. moved it there under the name growthCurve
simplified queries slightly
added capability to query material flow for a given commodity, facility class, and time span
provides functionality to graph material inflow and outflow curves as well as material inventory curves. closes #2.
fixed bug in facility lifetime query
adds capability to query material flow curves, and fixes small bugs in facility lifetime queries. testing still needs to be done on larger file, but any bugs can be fixed in a hotfix.