Drop cache setting

[gtrevisan]

• drop all CacheSetting classes
• drop cached_data and pre_filled_shot_data
• slightly revamp the logic behind the REQUIRED_COLUMNS (= coords) dataframe
• sort columns in final dataframe

[zapatace]

I ran two tests (efit time base and np.arange(0.9, 1.0, 0.001)) with 212 shots and compared the four dataframes, two by two, from the dev and drop-cache branches. In all cases, the dataframes have identical numerical values, though the column order differs. Lacking the expertise to analyze the code in depth (for now), I am satisfied with this result and will approve the merge.

[zapatace]

Happy with results of testing.