[INTERNAL] down sampled wav files

From 16-Bit 44kHz Stereo to 16-Bit 11kHz Mono.

Whole sound files now take less than 100 kByte instead of an half
MByte.

Change-Id: I611be8b0020835e16ca7ea2531dafbd4bb4ed7b3
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1671
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>