Rework code by using libmm-glib
Epic: https://source.puri.sm/Librem5/use-cases/issues/40, https://source.puri.sm/Librem5/use-cases/issues/44
Rewrite the plugin code by replacing g_dbus_proxy_calls with libmm-glib to make the code more rugged and handier to use for the implementation of further functionality, like delivery reports and the handling of offline SMS, etc.