Tests

[bharurn]

Following tests were added:

• mpt: Tests TopolDict, property generation in MPT, and selection in MPT
• prepare: Tests adding, deleting, and conversion of qmatoms dataframe to CPMD script
• gro: Reading gro files with 3 coords, and 6 coords (with forces). Time of execution is also checked
• vmd & pymol: VMD and Pymol packages mocked to test the 2 selectors
• topol: Some fixes added

setup.py was added Errors with the core algorithm discovered during testing also fixed.

To run the tests, pip install pytest, then navigate to the tests folder and run pytest.