Bugfix/cleanup2

[Gonzom]

Second cleanup pass.

This cleanup includes the following:

• Fixing errors: Typos, incorrect type annotation and other errors.
• Documentation: Documentation was added to missing functions and existing usages were updated to create a consistent documentation style.
• Code restructuring: Public functions were moved to the top of the file. Protected functions were added an underscore. Some functions were renamed to better reflect what they do, while others were split into smaller functions.
• A mypy.ini file was added.

[codecov-io]

Codecov Report

Merging #291 (5f01922) into develop (ea15719) will decrease coverage by 0.00%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #291      +/-   ##
===========================================
- Coverage    98.04%   98.04%   -0.01%     
===========================================
  Files           68       68              
  Lines         2964     2963       -1     
===========================================
- Hits          2906     2905       -1     
  Misses          58       58              

Impacted Files	Coverage Δ
app/internal/celebrity.py	100.00% <ø> (ø)
app/database/models.py	96.70% <100.00%> (ø)
app/internal/astronomy.py	100.00% <100.00%> (ø)
app/internal/daily_quotes.py	100.00% <100.00%> (ø)
app/internal/export.py	100.00% <100.00%> (ø)
app/internal/import_file.py	100.00% <100.00%> (ø)
app/internal/json_data_loader.py	100.00% <100.00%> (ø)
app/internal/languages.py	100.00% <100.00%> (ø)
app/internal/search.py	100.00% <100.00%> (ø)
app/internal/translation.py	100.00% <100.00%> (ø)
... and 9 more

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