Extinction Correction and Vega->STMAG Transform.

- Added extinction correction based on E(B-V) value
  from dwarf data table and A_X to E(B-V) values in
  Schlafly 2011.
- Converted Dartmouth isochrones from VegaMAG to STMAG
  using conversions in HST handbook (see blogpost from
  09/01/2014)