A USB webcam app using libuvc

Behaviour
---------

The app requests an USB session for accessing the webcam and a GUI session in
order to render the camera into.

Configuration
-------------

! <config enabled="yes" width="320" height="240" format="yuv" fps="30">
!   <vfs>
!     <dir name="dev"> <log/> <inline name="rtc">2018-01-01 00:01</inline> </dir>
!     <dir name="pipe"> <pipe/> </dir>
!  </vfs>
!  <libc stdout="/dev/log" stderr="/dev/log" rtc="/dev/rtc" pipe="/pipe"/>
! </conifg>

The frame format can be configured via the config attributes "width", "height",
"format", "fps". Currently the "yuv" and "mjpeg" formats are supported. The
"enabled" attribute allows for dynamic power on/off of the camera at runtime. In
case there is no suitable frame format present, the app will dump the camera
supported formats during startup.


