1PunMan authored May 28, 2018 and Victor Toso committed Jul 26, 2018

Currently lua plugins have no way of registering keys by themselves,
to use a new key it has to be added to system keys. This commit allows
lua plugins to register app-specific keys by itself by using
grl_data_set_for_id() and grl_data_add_for_id() introduced by Grilo in
0.3.6 release.

grilo#1