Other: Align error and warning syntax

[sandro-elsweijer]

Closes #2205

Describe your changes here:
The error and warning messages were all over the place, so I aligned them to be capitalized for easier readability.
A new check makes sure, that this is also enforced for future error and warning messages.

All these boxes must be checked by the AUTHOR before requesting review:

• The PR is small enough to be reviewed easily. If not, consider splitting up the changes in multiple PRs.
• The title starts with one of the following prefixes: Documentation:, Bugfix:, Feature:, Improvement: or Other:.
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As a reviewer please read through all the code lines and make sure that the code is fully understood, bug free, well-documented and well-structured.

General

• The reviewer executed the new code features at least once and checked the results manually.
• The code follows the t8code coding guidelines.
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Tests

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License

• The author added a BSD statement to doc/ (or already has one).

[codecov]

Codecov Report

❌ Patch coverage is 10.29412% with 61 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.25%. Comparing base (a4ae425) to head (eb645e0).

Files with missing lines	Patch %	Lines
src/t8_cmesh/t8_cmesh_io/t8_cmesh_save.cxx	0.00%	14 Missing ⚠️
src/t8_cmesh/t8_cmesh_io/t8_cmesh_readmshfile.cxx	0.00%	11 Missing ⚠️
src/t8_vtk/t8_vtk_write_ASCII.cxx	8.33%	11 Missing ⚠️
src/t8_cmesh/t8_cmesh_io/t8_cmesh_triangle.cxx	0.00%	6 Missing ⚠️
..._geometry_implementations/t8_geometry_lagrange.cxx	0.00%	6 Missing ⚠️
src/t8_vtk/t8_vtk.c	0.00%	6 Missing ⚠️
src/t8_cmesh/t8_cmesh.cxx	0.00%	3 Missing ⚠️
src/t8_cmesh/t8_cmesh_internal/t8_cmesh_copy.c	0.00%	1 Missing ⚠️
src/t8_geometry/t8_geometry.cxx	0.00%	1 Missing ⚠️
src/t8_geometry/t8_geometry_base.hxx	0.00%	1 Missing ⚠️
... and 1 more

Additional details and impacted files

@@               Coverage Diff               @@
##           fix-scripts    #2204      +/-   ##
===============================================
+ Coverage        78.23%   78.25%   +0.01%     
===============================================
  Files              114      114              
  Lines            19034    19050      +16     
===============================================
+ Hits             14891    14907      +16     
  Misses            4143     4143              

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