Bug 34613: Replace onclick attributes in midiplayer.js

Bug 34613: Replace onclick attributes in midiplayer.js

This patch replaces the onclick attributes in midiplayer.js
with Javascript click handlers.

To test:
0. Apply patch
1. Clear browser cache (it may be necessary to go into the
   Network tab and explicitly disable cache)
2. Add 031 subfields 2gopnu to Default framework
3. Create a catalogue record with a 031 like follows:
2: pe
g: G-2
o: 4/4
p: 4bB''C2bE/2F4GbB/'bB2''C4D/F2.bE/4GG2bB/4'''C2C4''bB/4bE2G4bB/4bE2.F/
n: xFCGD
4. Enable the following sysprefs:
   OPACShowMusicalInscripts
   OPACPlayMusicalInscripts
5. Go to OPAC record view and click "Play this sample"
6. Play with the "Pause/Start" and "Stop" buttons
7. If the buttons work, it means the patch worked

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>