add dead time

[mdoucet]

Add dead time.

The option is currently set to True. Should add a settings panel like we did for refred

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 44.31818% with 98 lines in your changes missing coverage. Please review.

Project coverage is 35.49%. Comparing base (04e625c) to head (2d32bcc).
Report is 20 commits behind head on next.

❗ Current head 2d32bcc differs from pull request most recent head 23f9b00

Please upload reports for the commit 23f9b00 to get more accurate results.

Files	Patch %	Lines
..._ui/interfaces/data_handling/DeadTimeCorrection.py	22.41%	45 Missing ⚠️
...ectivity_ui/interfaces/data_handling/instrument.py	10.00%	36 Missing ⚠️
reflectivity_ui/ui/deadtime_settings.py	57.69%	11 Missing ⚠️
reflectivity_ui/interfaces/main_window.py	61.53%	5 Missing ⚠️
...flectivity_ui/interfaces/data_handling/data_set.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next      #85      +/-   ##
==========================================
+ Coverage   35.28%   35.49%   +0.21%     
==========================================
  Files          30       33       +3     
  Lines        6054     6260     +206     
==========================================
+ Hits         2136     2222      +86     
- Misses       3918     4038     +120     

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