QMThermo unittest skips test if your MOPAC executable is unaccessible

Testing the qmdata generation and that we can get
thermodynamic values from it. Checks that your MOPAC
executable is accessible, otherwise the test is
skipped.
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.
QMTP tests for Gaussian.

Essentially the same thing as the MOPAC test.
Removed check for the QM scratch directory

The scratch directory is not a requirement, so it
should not throw an error if it fails.
Tests for the main qm script
Added PM6 and PM7 tests.

Now that these have been added, they need to be tested.
Check that no files are in the test output folder.

If there are files, delete them. This ensures the test
runs through the running of a QM job, and doesn't load a
`.thermo` file  (this is tested elsewhere) from a previous test.
QMTP tests without environment variables

The tests ran with an 'RMGpy' environment variable,
but this is not always set, so the tests can now be run
without the variable defined.
Fix the rmgpy getPath method so the test can find the testing folder

rmgpy.getPath was not properly set
Checks for and makes folder to store qm testing files.
Merge pull request #228 from pierrelb/QMTPtest

QMTP tests now implemented and passing.