Issue983 xaxis q cplot

[jhmigueles]

Closes #983 => Horizontal axis of QC plot is now redefined to make cleares the days length and also marking midnights and noons.

Checklist before merging:

• Existing tests still work (check by running the test suite, e.g. from RStudio).
• Added tests (if you added functionality) or fixed existing test (if you fixed a bug).
• Updated or expanded the documentation.
• Updated release notes in inst/NEWS.Rd with a user-readable summary. Please, include references to relevant issues or PR discussions.
• Added your name to the contributors lists in the DESCRIPTION file, if you think you made a significant contribution.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ededec3) 78.41% compared to head (5777400) 78.44%.
Report is 12 commits behind head on master.

❗ Current head 5777400 differs from pull request most recent head 8970c07. Consider uploading reports for the commit 8970c07 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #985      +/-   ##
==========================================
+ Coverage   78.41%   78.44%   +0.02%     
==========================================
  Files          99       99              
  Lines       13371    13386      +15     
==========================================
+ Hits        10485    10500      +15     
  Misses       2886     2886              

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