Bug 36051: Add option to specify SMS::Send driver parameters in a system preference

Bug 36051: Add option to specify SMS::Send driver parameters in a system preference

If an SMS::Send driver ( such as Twilio ) requires additional parameters, those
parameters have to be placed in a yaml file named after the SMS::Send driver,
and the path to that file specified in the Koha conf file.

It would be good if we had the option to specify those parameters in a YAML
system preference instead. This would be less complicated and avoid requiring
an administrator to update that data from the backend.

Test Plan:
1) Set up an SMS::Send driver that requires additional options;
   a Twilio account meets these requirements and can be created for
   free. Set this up using the traditional file based system.
2) Verify you can send SMS messages
3) Move the contents of that file into the new system preference
   SMSSendAdditionalOptions
4) Verify you can still send SMS messages
5) Delete the file
6) Verify yet again you can still send SMS messages!

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>