Add grid settings

[joergbrech]

Description

Fixes #1220.

This PR adds the option to set the grid resolution via the settings. Currently, the settings are not preserved and are reset to default values each time TiGL opens. You can set the origin and grid spacing of the grid. The settings are accessible via the cog wheel / Settings menu.

How Has This Been Tested?

GUI only

Checklist:

Task	Finished	Reviewer Approved
At least one test for the new functionality was added.	yes does not apply	OK
New classes have been added to the Python interface.	yes does not apply	OK
The code is properly documented with doxygen docstrings	yes does not apply	OK
Changes are documented at the top of ChangeLog.md	yes does not apply	OK

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.47%. Comparing base (4332bda) to head (f44afb1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1269   +/-   ##
=======================================
  Coverage   72.47%   72.47%           
=======================================
  Files         313      313           
  Lines       27391    27391           
=======================================
  Hits        19851    19851           
  Misses       7540     7540           

Flag	Coverage Δ
unittests	72.47% <ø> (ø)

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