Cleanup of visibility (u,v) points definition

[paolomassa]

• Merged 'get_visibility_info_giordano' and 'get_visibility_info' into 'get_uv_points_data'
• Removed 'correct_phase_projection' since it is not needed with the new definition of (u,v) points
• Added 'test_visibility.py' (and removed 'test_visibility.bk')
• Updated 'imaging_demo.py' to be consistent with the new definition of (u,v) points

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 64.03%. Comparing base (d72c4c1) to head (e8759a2).

:exclamation: Current head e8759a2 differs from pull request most recent head da2b611. Consider uploading reports for the commit da2b611 to get more accurate results

Files	Patch %	Lines
stixpy/calibration/visibility.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #98 +/- ## ========================================== + Coverage 62.12% 64.03% +1.90% ========================================== Files 29 29 Lines 1769 1746 -23 ========================================== + Hits 1099 1118 +19 + Misses 670 628 -42 ```

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