DEV-40702: fixed the audio device enumeration code so that it works

with Vivox V2 and V3 SDKs. We were assuming that the <CaptureDevice>
tag contains only a single tag (<Device>), but the V3 SDK returns
other tags such as <DisplayName> and <Type>.

I also added the current Vivox SDK version to the About window so that
it is easier to tell which version your client is actually using.