Testing Framework and initial tests

[mpatrou]

It includes the testing framework, tests and some other improvements

Short description of the changes:

It includes:

• pytest configurations
• initial tests for main window, application start, version, configuration settings
• argument parsing

Long description of the changes:

Check list for the pull request

• I have read the [CONTRIBUTING]
• I have read the [CODE_OF_CONDUCT]
• I have added tests for my changes
• I have updated the documentation accordingly

Check list for the reviewer

• I have read the [CONTRIBUTING]
• I have verified the proposed changes
• best software practices
  • all internal functions have an underbar, as is python standard
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

Manual test for the reviewer

References

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 63.69%. Comparing base (1978169) to head (2edbc71).

Files with missing lines	Patch %	Lines
src/hyspecplanningtools/hyspecplanningtools.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            next       #2       +/-   ##
==========================================
+ Coverage   1.60%   63.69%   +62.09%     
==========================================
  Files          4        8        +4     
  Lines        125      157       +32     
==========================================
+ Hits           2      100       +98     
+ Misses       123       57       -66     

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