Add initial implementation of sound effects feature

Adds a sound effect player class which listens for the following events from the voice recognizer:
- Command Accepted
- Command Rejected
- Listening Started
- Listening Stopped

Sound file locations are currently hard-coded and only WAV files are supported (due to the use of System.Media.SoundPlayer).
Add sound effect UI and clean up initial implementation.
Merge branch 'development' of https://github.com/flyingcroissant/articulate into feature/soundeffects

Conflicts:
	Articulate/MainWindow.xaml.cs

Merge in changes since creating feature branch.
Remove unused method.
Merge remote-tracking branch 'flyingcroissant/feature/soundeffects' into development
Code style changes for MainWindow