Changed the lifetime of the default MIDI oputput.
Removed the need for Timer workaround in AudioDeviceSelectorComponent.

Previously, the samplerate combo would display as a blank box in the
case that the device's actual samplerate wasn't one of the "available"
samplerates reported by the device.

- Add AlertWindow::show() and showAsync() methods that take a MessageBoxOptions argument
  - Add NativeMessageBox::show() and showAsync() methods that take a MessageBoxOptions argument
  - Update the DialogsDemo to demonstrate the new methods
  - Deprecate AlertWindow::showNativeDialogBox() in favour of the NativeMessageBox methods
  - Pass button strings specified in MesssageBoxOptions to native dialog boxes correctly
  - Use modern TaskDialog on Windows for the native dialog box where available

This fixes an issue where non-ascii characters in channel and MIDI
device names were not drawn correctly.