Implement voice calls over QMI

The aim is to implement basic single call functionality over QMI. So far, implemented starting a call, receiving an incoming call, accepting it and hanging up call. Seems to work fairly well in my Poco F1 (SDM845) running pmOS.

This is an early draft so I can get feedback on whether I am doing this right. It's my first time writing glib and MM code. Not to mention, I am touching c programming after long years. Kindly help me if I didn't handle things properly and ensure I have handled the pointers properly.

There are some !!!FIX ME!!! for which I needed answer. I will probably start a code review for it.