Make sound files choosable through the UI

[aliciasprig]

Currently it will choose to sound file to play in the following order.

• The file name stored in the settings.ini key "Global/Sounds/"
• The file "./sounds/<soundname.wav>" (this is the 0.8.x behaviour)
• Or if the previous don't work it will use the resource file ":/sounds/<soundname.wav>"
  Presently there is no mechanism in the UI to choose the filename stored in the key "Global/Sounds/".

A label, text box and browse button should be added for each sound type to the "Sound" tab of the global settings dialog.