Video call - Restcomm API

Allow video calls through `Calls` REST API.

Planned tasks
---
- [ ] Adapt database entities and MyBatis layer
- [ ] Adapt `CallsEndpoint`
- [ ] Adapt converters
- Tests:
- [ ] Initiate a video call through Restcomm API.
- [ ] SIP agent should ring and play video-play.xml
- [ ] Initiate a video call from already established audio call
- [ ] Remove video stream from the video call