Bug 20212: Use API to render orders datatable

Bug 20212: Use API to render orders datatable

This patch makes the pending orders datatable render using the API
instead of hte old controller script. It implements native server-side
pagination thanks to the API and the datatables wrapper.

On polishing it, we found that data can contain many null values, and it
got dirtier in the process.

This code with all the checks that are done on the data is the result of
testing this dev with real-life production databases, huge ones with
thousands of orderlines.

To test:
1. You should compare the behaviour between this table, and the original
   one in master.

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Andrew Fuerste-Henry <andrew@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>