Add Simulation

[PProfizi]

Refactors Solution to Simulation. Adds load_simulation command.

One drawback is that users would have to change the load_solution command in their scripts to load_simulation. But then again, with all the changes we will make, they will have to change their scripts anyway and this way it would make a clear difference as to which version they are using.

This also wraps FieldsContainer with DataObject instead of inheriting, solving a memory issue and simplifying manipulation of the fields_container.

This then fixes DataObject.as_array and as_dataframe so that docstring tests pass.

[codecov[bot]]

Codecov Report

Merging #225 (31ca640) into post_refactor (9346236) will decrease coverage by 2.00%. The diff coverage is 20.83%.

@@                Coverage Diff                @@
##           post_refactor     #225      +/-   ##
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- Coverage          76.89%   74.89%   -2.01%     
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  Files                 30       30              
  Lines               1632     1665      +33     
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- Hits                1255     1247       -8     
- Misses               377      418      +41