Simplify audio settings page

Audio settings are hard to get right on Windows, where there are several
host APIs (MME, DirectSound, WASAPI, and WDM KS).  In particular, users
are faced with too many non-working settings combinations.

This patch tries to simplify this by implementing better defaults and
only displaying sample rates that are supported by the devices.

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Use Qt5 Q_OS_* macros instead of Q_WS_*

The Q_OS_* macros should be used instead of Q_WS_* in Qt5:
https://qt-project.org/doc/qt-5.0/qtdoc/portingguide.html

Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>