Implement dynamic tracks addition with renegotiation (#27)

[evdokimovs]

Part of #27

Required for #89

Synopsis

We need to implement renegotiation functional for ICE restarts (#89) and MediaTracks updating (adding new Endpoints to an already going call).

Solution

• 1. Add RenegotiationStarted and SdpOfferMade Events.
• 2. Implement renegotiation on a server side
• 3. Lock Peer's state until renegotiation finish (will be done in a separate PR)
• 4. Implement renegotiation on a client side

Checklist

• Created PR:
  • In draft mode
  • Name contains WIP: prefix
  • Name contains issue reference
  • Has k:: labels applied
  • Has assignee
• Documentation is updated (if required)
• Tests are updated (if required)
• Changes conform code style
• CHANGELOG entry is added (if required)
• FCM (final commit message) is posted
  • and approved
• Review is completed and changes are approved
• Before merge:
  • Milestone is set
  • PR's name and description are correct and up-to-date
  • WIP: prefix is removed
  • All temporary labels are removed

[evdokimovs]

FCM

Implement dynamic tracks addition with renegotiation (#105, #27)

- support adding new endpoints to the already interconnected Members
- implement PeerConnection renegotiation
- add TracksApplied event