audiotrack: increase audio latency

Queue more than one audio buffer at a time (limit of 1 second). TimeGet will
report a bigger delay, but the module will be more stable and more efficient.

AudioTrack delay is now calculated by JNIThread when a buffer is written.
Overall delay is calculated in TimeGet by adding AudioTrack delay and queued
delay.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>