Bug 15734: Use To.json to filter audio alerts

Bug 15734: Use To.json to filter audio alerts

Test Plan:
1) Enable audio alerts
2) Note audio alerts don't work
3) Apply this patch
4) Note audio alerts now work

Use complex selectors to test:
  #circ_returns p.problem:contains('Not checked out.')
  #doc3 > #bd

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 58314233f70fd9fd2f2830250ff0362e369b6ff1)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit e635b63e94c0dd09f20c936039d518c3e494252c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>