Merge pull request #243 from bslakman/master

Solvation unit tests looks good to me. Tests all seem to pass.
Notice that:
    SolvationDatabase.solventLibrary
    SolvationDatabase.soluteLibrary
have been replaced with:
    SolvationDatabase.libraries['solvent']
    SolvationDatabase.libraries['solute']
which makes things more consistent with other types of database.
add missing method argument in thermoEstimator example input file

This crashed the thermoEstimator.
Make statmech depositories a dictionary.

Now it is consistent with thermo depositories.  Otherwise
it does not make sense to store a default dictionary but then
replace with the StatmechDepository object.  Also this allows us
to add more depositories in the future as necessary.
Fix statmech groups saving error.

Groups cannot be saved directly. self.groups is a dictionary.
Implement getAllSoluteData method in solvation.

This returns all the possible solute descriptors for a species, which if in the library, includes the library set, and always includes the group additivity estimate.
Better documentation for some solvation methods.

Added information about units for the solvation correction to thermo.