[ENH] 2D Correlation Spectroscopy widget

[borondics]

Picked up this project from many years ago.

• made it work again
• data sorting handled
• graph cosmetic changes

[codecov-commenter]

Codecov Report

Merging #665 (404ff67) into master (0b29299) will decrease coverage by 0.58%. Report is 4 commits behind head on master. The diff coverage is 62.90%.

:exclamation: Current head 404ff67 differs from pull request most recent head 5746900. Consider uploading reports for the commit 5746900 to get more accurate results

@@            Coverage Diff             @@
##           master     #665      +/-   ##
==========================================
- Coverage   89.28%   88.71%   -0.58%     
==========================================
  Files          72       72              
  Lines       12120    12162      +42     
==========================================
- Hits        10821    10789      -32     
- Misses       1299     1373      +74