Fix bug where default audio device was used for notifications.

Caused by the isAccessible check in AudioSystem failing.
The fix is just to remove this check (as discussed with lubo over IM)
Fixes multiple issues related to unplugging the last audio device and then plugging it back.
Updates VideoLayout so that it doesn't show invisible components.
Makes it possible to override mutability of properties from the overrides file.
Makes the display of the video formats by webcams on Windows more useful (to developers).
Adds support for Logitech HD Pro Webcam C920 on Windows.
Optimizes the video capture on Windows by avoiding an unnecessary copy of the video frames.
Fixes a problem where video wouldn't work in a jitsi-hosted
conference. Adds some logs.

We don't need to perform any format checks in
VideoMediaDeviceSession#onRTCPFeedbackCreate(). At the time of a call,
our format could be null (for MediaStreamMediaDeviceSession's
subsequently added to a VideoTranslatorMediaDevice), which causes an
NPE.
Fixes a problem with multiple Player instances created for local video
playback, on the focus of a video conference (which also lead to multiple
Components and renderers being used), which sometimes caused the videos
on the focus' interface to freeze.

Prevents MediaStreamMediaDeviceSession from creating local
Player instances, instead reuses the Player from the
VideoTranslatorMediaDevice's wrapped VideoMediaDeviceSession.

Makes VideoTranslatorMediaDevice a VideoListener of its wrapped
VideoMediaDeviceSession, forwarding all received events to all of its
MediaStreamMediaDeviceSession's.
Fixes an access violation during the initialization of the PortAudio integration. Reported by Tudor Berechet.
Makes failures in default property loading sound less alarming.
Prevents invalid RTP/RTCP packets from being handled (for example empty hole
punch packets being transformed by ZRTP).
Relaxes checks for validity in RawPacket, because some RTCP packets are
mistakenly flagged invalid.
Improves AudioMixer for one-to-one calls, strives towards pass-through behavior.
Improves the garbage collection profile of AudioMixer.