[MRH & RW]: Updated BathGas.java
[MRH & RW]: Updated BathGas.java

Before: The order in which colliders was accessed was random (HashMap).  Therefore, if one species and one inert gas existed (CH4 & N2, in the HXD13 test case), the MW would either be that of N2 (if the order accessed by CH4, N2) or ~29.7 (MW_N2 + mf*MW_CH4).  Also, epsilon for an inert gas was defined by getSigma()

Now: The MW, ExpDown, Sigma, Epsilon for the BathGas are weighted sums of all colliders.  Since the sigma/epsilon parameters are not known (in RMG) for He and Ar, we print a message stating so.

enochd/RMG-Java,keceli/RMG-Java,jwallen/RMG-Java,KEHANG/RMG-Java,connie/RMG-Java,keceli/RMG-Java,faribas/RMG-Java,connie/RMG-Java,jwallen/RMG-Java,KEHANG/RMG-Java,rwest/RMG-Java,enochd/RMG-Java,KEHANG/RMG-Java,connie/RMG-Java,rwest/RMG-Java,keceli/RMG-Java,jwallen/RMG-Java,nyee/RMG-Java,nyee/RMG-Java,keceli/RMG-Java,nyee/RMG-Java,ReactionMechanismGenerator/RMG-Java,nyee/RMG-Java,faribas/RMG-Java,ReactionMechanismGenerator/RMG-Java,nyee/RMG-Java,faribas/RMG-Java,ReactionMechanismGenerator/RMG-Java,KEHANG/RMG-Java,nyee/RMG-Java,rwest/RMG-Java,enochd/RMG-Java,keceli/RMG-Java,jwallen/RMG-Java,KEHANG/RMG-Java,ReactionMechanismGenerator/RMG-Java,faribas/RMG-Java,jwallen/RMG-Java,enochd/RMG-Java,jwallen/RMG-Java,ReactionMechanismGenerator/RMG-Java,enochd/RMG-Java,KEHANG/RMG-Java,keceli/RMG-Java,rwest/RMG-Java,enochd/RMG-Java,connie/RMG-Java,connie/RMG-Java,rwest/RMG-Java