Working GaussianTypeElectronInteractionIntegral. Increased requirement
for BoysFunction precision in HermiteIntegral.
Restructuring of files and tests
Moved gaussian classes to basisfunctions/gaussian/integrals
Modified class names from GaussianType* to Gaussian*
Restructured ElectronSystem to use coupledIntegral and uncoupledIntegral
instead of kineticIntegral and nuclearAttractionIntegral.