Addition of dipole polarizability data for isolated atoms

[alejandragallego-M]

I added the static dipole polarizability data for isolated atoms reported in https://doi.org/10.1080/00268976.2018.1535143 to their respective files. During testing, I observed an issue in the code: it is loading compiled data instead of data directly from the files.

[gabrielasd]

Hi @alejandragallego-M (and @PaulWAyers )

With the updated csv files, the new polarizability values will be accessible through instances of the Elements class in the periodic module: https://github.com/theochem/AtomDB/blob/c39ecd925391a0efdcc9a3f7d9573ff3231cf23d/atomdb/periodic.py#L258

This can be tested updating the periodic module tests: https://github.com/theochem/AtomDB/blob/c39ecd925391a0efdcc9a3f7d9573ff3231cf23d/atomdb/test/test_periodic.py#L49

With regards to the issue: ``During testing, I observed an issue in the code: it is loading compiled data instead of data directly from the files." This to me is the expected behaviour based on the current implementation. Instances of the Species class for a given database, only show information loaded from already compiled data. So to have the updated polarizabilities available for all databases through instances of the Species class we will need to recompile the neutral species for each database.

[gabrielasd]

I will merge these changes into a branch of master so that the broken tests from the periodic module can be fixed.