Add support for saving and loading geotables in CSV format

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (32b553d) 93.52% compared to head (9c19ff9) 93.52%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #38 +/- ## ======================================= Coverage 93.52% 93.52% ======================================= Files 11 12 +1 Lines 494 525 +31 ======================================= + Hits 462 491 +29 - Misses 32 34 +2 ```

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