Nuclear potential

[Christian48596]

Introduced 3 models for finite charge nucleus and modified the actual finite charge nucleus model to consider many atom system.

It is early to be merged to master. I am working on reading of parameters by json file.

[stigrj]

Made some small fixes, and now it's able to run the three different models and produces reasonable results. The model can be chosen by the input parameter

WaveFunction {
  nuclear_model = 3     # 1=HFYGB, 2=Sphere, 3=Gaussian
}

[codecov[bot]]

Codecov Report

Patch coverage: 5.34% and project coverage change: -0.23 :warning:

Comparison is base (9a08907) 69.53% compared to head (2920dbb) 69.31%.

:exclamation: Current head 2920dbb differs from pull request most recent head 76e106d. Consider uploading reports for the commit 76e106d to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #439 +/- ## ========================================== - Coverage 69.53% 69.31% -0.23% ========================================== Files 175 183 +8 Lines 14852 15618 +766 ========================================== + Hits 10327 10825 +498 - Misses 4525 4793 +268 ``` | [Impacted Files](https://app.codecov.io/gh/MRChemSoft/mrchem/pull/439?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MRChemSoft) | Coverage Δ | | |---|---|---| | [src/qmoperators/one\_electron/NuclearOperator.cpp](https://app.codecov.io/gh/MRChemSoft/mrchem/pull/439?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MRChemSoft#diff-c3JjL3Ftb3BlcmF0b3JzL29uZV9lbGVjdHJvbi9OdWNsZWFyT3BlcmF0b3IuY3Bw) | `35.67% <0.00%> (-56.73%)` | :arrow_down: | | [src/qmoperators/one\_electron/NuclearOperator.h](https://app.codecov.io/gh/MRChemSoft/mrchem/pull/439?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MRChemSoft#diff-c3JjL3Ftb3BlcmF0b3JzL29uZV9lbGVjdHJvbi9OdWNsZWFyT3BlcmF0b3IuaA==) | `100.00% <ø> (ø)` | | | [src/driver.cpp](https://app.codecov.io/gh/MRChemSoft/mrchem/pull/439?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MRChemSoft#diff-c3JjL2RyaXZlci5jcHA=) | `72.75% <77.77%> (+0.10%)` | :arrow_up: | ... and [89 files with indirect coverage changes](https://app.codecov.io/gh/MRChemSoft/mrchem/pull/439/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=MRChemSoft)

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[stigrj]

Superseeded by #453