Add keyboard shortcuts

[chidiwilliams]

• Adds keyboard shortcuts for a variety of actions
• Adds a preferences window for viewing and managing shortcuts
• Click 'Enter' to open the viewer for a transcription

Resolves #404

[codecov]

Codecov Report

Merging #409 (4a95507) into main (474f4c5) will increase coverage by 0.98%.
The diff coverage is 90.76%.

@@            Coverage Diff             @@
##             main     #409      +/-   ##
==========================================
+ Coverage   76.84%   77.82%   +0.98%     
==========================================
  Files           9       15       +6     
  Lines        1766     1917     +151     
==========================================
+ Hits         1357     1492     +135     
- Misses        409      425      +16     

Flag	Coverage Δ
Linux	77.56% <89.13%> (+0.95%)	⬆️
Windows	74.31% <90.21%> (+1.32%)	⬆️
macOS	76.05% <89.67%> (+1.14%)	⬆️

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Impacted Files	Coverage Δ
buzz/widgets/shortcuts_editor_widget.py	81.25% <81.25%> (ø)
buzz/assets.py	83.33% <83.33%> (ø)
buzz/gui.py	77.75% <88.52%> (+0.02%)	⬆️
buzz/locale.py	100.00% <100.00%> (ø)
buzz/settings/settings.py	100.00% <100.00%> (ø)
buzz/settings/shortcut.py	100.00% <100.00%> (ø)
buzz/settings/shortcut_settings.py	100.00% <100.00%> (ø)
buzz/widgets/preferences_dialog.py	100.00% <100.00%> (ø)

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