Added trivial tests for dark.aa properties.

Fixes #225 
Would it make more sense / would it work to do from dark.aa import (PROPERTIES, ACIDIC, ALIPHATIC, AROMATIC, BASIC_POSITIVE, HYDROPHILIC, HYDROPHOBIC, HYDROXYLIC, NEGATIVE, NONE, POLAR, SMALL, SULPHUR, TINY) as individualProperties.
And then do self.assertEqual() on that (just in case we add another property and forget to change it in the test).