v1.7.15

-- Fix matlab error in hmrR_BlockAvg and DataClass.AddChannelDod() method when calculating dodAvg
-- Fix another separate matlab error in hmrG_BlockAvg when calculating dodAvg for group
-- Bring back hmr.guiControl.datatype because it is useful to have for sharing with other GUIs but continue to use getDatatype() function within Homer3 GUI.