New PJSUA & PJSUA2 APIs for instantiating extra audio device

[nanang]

The APIs will be useful for application that needs to work with multiple sound devices concurrently. It can also help application to simplify the tasks of improving media framework clock as described here.

Specifications

1. Audio device settings to be supported:
   • PJSUA: ​pjmedia_snd_port_param.
   • PJSUA2: playback and record device IDs.
2. Application can apply further settings whenever needed by:
   • PJSUA: querying the sound device port and apply further settings directly to it using PJMEDIA Sound Device Port APIs.
   • PJSUA2: inheriting the class ExtraAudioDevice.
3. Audio device must be registered to the conference bridge. For PJSUA it must have API to query the conference bridge port. For PJSUA2, it must be descendant of ​AudioMedia.