Add shortcut for audio panel (#15497)
Fixup of #15472
Summary of the issue:
A default gesture to open the new audio panel is desirable
Description of user facing changes
Adds nvda+ctrl+u as a command to open the audio panel
Commands for opening settings panels are now included in the key commands doc
Description of development approach
Adds nvda+ctrl+u as a command to open the audio panel
Adds keyCommands to the appveyor build for easier review of changes.
Updates to user guide
