GPII-182: Removing call to g_type_init

g_type_init function has been deprecated since glib version 2.36,
see: https://developer.gnome.org/gobject/stable/gobject-Type-Information.html#g-type-init
GPII-182: Declare variant and type just once

This change fixes the "variable ‘type’ set but not used" warning
GPII-182: Add a return value to get_gsetting function

This change fixes the "control reaches end of non-void function" warning
Merge remote-tracking branch 'javihernandez/GPII-182'