Use chemical formula if species label not present in getSpeciesIdentifier function
getAtomType unittest fix

Not an important fix, but the previous test returned None for
the noble gases, but with rdKit this is no longer true.
This fixes that test.
Some unittests for QMThermo module

Testing the qmdata generation and that we can get
thermodynamic values from it. More specific methods
need to be added.
Remove output files when first testing QMTP with MOPAC

If an output file exists from a previous run, the method
will to read the `.thermo` file printed from that
run, and not test the rdKit molecule generation nor the
MOPAC specific methods. Removing it ensures `testGenerateQMData`
covers these methods, while `testGenerateThermoData` will cover
the use of an existing `.thermo` file.
Check that your MOPAC installation is accessible

Checks that your MOPAC environment variables are correctly
declared.
QMTP tests for Gaussian.

Essentially the same thing as the MOPAC test.