Feat calibration fixes

[paolomassa]

• Implemented background subtraction in the demo
• Fixed ELUT correction
• Implemented ELUT correction for background counts
• Implemented Energy Edge Masks

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 83.33333% with 8 lines in your changes missing coverage. Please review.

Project coverage is 68.47%. Comparing base (d44a1c8) to head (b88fdb5). Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
stixpy/map/stix.py	14.28%	6 Missing :warning:
stixpy/calibration/visibility.py	93.93%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #106 +/- ## ========================================== + Coverage 66.33% 68.47% +2.13% ========================================== Files 31 31 Lines 1821 1843 +22 ========================================== + Hits 1208 1262 +54 + Misses 613 581 -32 ```

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