WIP Statmech calc revisions

[davidfarinajr]

This is a WIP PR for statmech calculator. This PR includes several revisions to the statmech calculator including:

• changed directory attr to ts_directory and species_directory
• added function to calculate E0 using arkane Gaussian parser.
• added function to calculate energy "wells" of reactants, TS, and products (and check for negative barrier height)
• added function (and option to choose) the exothermic direction for determining kinetics
• added atom and bond corrections
• added hindered rotor option (but this needs more work to implement)
• use cclib parser mult from log file instead of rmgpy.molecule mult
• added bromine to symbol dict
• init a statmech calc with autotst.reaction.Reaction or a rxn str