Port grabbing and Modem object creation

Once a port passes all probing filters of a given plugin, the plugin will grab the port. When the first port of a given device is grabbed, the plugin will create the required Modem object.

While preparing to get the Modem object grab the specific port probed, udev-based port type hints can be used to specify AT port flags (e.g. if a port is to be considered primary, secondary or for PPP).