Add T-dep solubility prediction method using T-dep Hsolution

[yunsiechung]

Hi, I implemented the methods for predicting T-dep solubility using the T-dep Hsolution method. Since this method is only applicable to the solvents in the database and valid temperature ranges, if the calculation cannot be performed, it's skipped and error message is generated. You can check test this by running calculate_solubility.py.

Some of other changes include:

• All codes are moved to the correct directory named "solvation_predictor" so that the module imports can be done properly.
• Cache python files are added to .gitignore because these are newly created whenever the code are run and they are usually ignored in git.

Could you review and merge this? Thanks!

[yunsiechung]

@fhvermei I made additional commits. They include:

• Make logging optional. And if logger file is not provided, it will print out the logging messages instead. This commit is added such that an empty class object can be created.
• Give dGsolv_T and dSsolv_T as outputs.
• Add options to validate more input data, such as reference_solvent, reference_solubility, and temperature. For reference_solubility and temperature, validate function will check whether they are numeric. A user has an option to select the list of input data to validate.
• Your previous validate function will replace the input solvent and solute SMILES with the new ones that are generated by rdkit function. While this is necessary for converting InChI to SMILES, this might make the user confused because the output file no longer contains the original solvent and solute inputs they provided, and the orders of the df rows are sometimes changed if any of the input row contains wrong SMILES. To avoid this confusion, if validate function is used, the original solvent, solute, and reference_solvent SMILES are stored as separate columns in the output file.
• An option to provide a dictionary containing solvent's critical properties is added. If this option is not used, the default dictionary is used.
• Some column and object names are changed (e.g. changing dHsolu to dHdiss)
• A warning message is displayed to recommend the T-dep Hdiss option whenever the temperature is above 350 K.