libqmi-glib,qmicli: added new Telit General Modem Service (GMS).

Added Telit's General Modem Service to libqmi-glib.

Messages supported: QMI_GMS_TEST_SET_VALUE and QMI_GMS_TEST_GET_VALUE.

Also in qmicli, added corresponding commands:

--gms-test-get-value

--gms-test-set-value=[mandatory-value][,[optional-value]]

It seems to work (see pic), but I (again) suggest you to treat my commits carefully at least in the beginning since I'm not terribly experienced with C (sorry) :)