Refactored and updated TestLattice class.

Added tests for new single inversion functions.
Added code to compare against precomputed configurations
and propagators.
Added prop and config data to use in tests.
Refactored TwoPoint test class

Updated to use np.allclose instead of manual check
Now uses create_fullpath function to generate data file names
Renamed test data to something more consistent with other file names for
consistency.
Added missing test data files.