Implement call quality estimation (#27)

[evdokimovs]

Part of #27

Synopsis

We need to measure call quality and provide information about current score to the JS side.

Solution

Quality score will be calculated based on Algorithm::MOS, which is derived from E-model, introduced in ITU-T G.107 with some simplifications and tweaks.

• [x] Store RTC stats within some period at the server and periodically calculate and send quality score to the Jason
• [x] Add Room.on_quality_score_update callback to the Jason into which call quality updates will be provided

Checklist

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

[evdokimovs]

FCM

Implement call quality estimation (#132, #27)

- calculate connection quality based on client RTC stats
- add 'ConnectionHandle.on_quality_score_update' callback to Jason