restructure of files, oh, and also PSRK Ge Model

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.59218% with 24 lines in your changes missing coverage. Please review.

Project coverage is 93.37%. Comparing base (b5232a3) to head (4d43ac9). Report is 13 commits behind head on dev.

Files with missing lines	Patch %	Lines
...cess_gibbs/group_contribution/model_parameters.f90	18.18%	9 Missing and 9 partials :warning:
...elmholtz/cubic/implementations/implementations.f90	66.66%	2 Missing and 1 partial :warning:
...ibbs/group_contribution/temperature_dependence.f90	92.85%	0 Missing and 2 partials :warning:
.../models/excess_gibbs/group_contribution/groups.f90	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #113 +/- ## ========================================== - Coverage 93.77% 93.37% -0.40% ========================================== Files 59 65 +6 Lines 2731 2899 +168 Branches 198 212 +14 ========================================== + Hits 2561 2707 +146 - Misses 128 139 +11 - Partials 42 53 +11 ```

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