Add a QAudioBuffer class.

Prereq for probing or decoding.  The abstract API probably needs
to change.

Change-Id: Ie0bf796c1f581f34bbc0a8af2dffc387c513a330
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

tests/auto/unit/multimedia.pro

@@ -29,6 +29,7 @@ SUBDIRS += \
     qvideoframe \
     qvideosurfaceformat \
     qwavedecoder \
+    qaudiobuffer
 
 # Tests depending on private interfaces should only be built if
 # these interfaces are exported.
@@ -36,3 +37,4 @@ contains (QT_CONFIG, private_tests) {
     SUBDIRS += \
         qdeclarativeaudio
 }
+