LP#1691860 Webstaff audio alert nosound.wav

LP#1691860 Webstaff audio alert nosound.wav

Adds a small nosound.wav file which may be used by administrators to
silence a specific alert for all users on the server.

To test:

[1] mkdir -p /openils/var/web/audio/notifications/success/patron/
[2] cd /openils/var/web/audio/notifications/success/patron/
[3] ln -s ../../nosound.wav by_search.wav
[4] Perform a patron search in the browser client and confirm no sound
    is played upon successful search.

If patron searches have recently been performed, step 4 may require a
cache clear, a different tab, browser restart, eye of newt.

Signed-off-by: Bill Erickson <berickxx@gmail.com>