Issue 191 viewer app multi source grid layout

[jackshen]

Issue: https://github.com/dolbyio-samples/rts-app-react-publisher-viewer/issues/191

Description

In this PR, you can:

• View up to 4 sources in viewer
• All 4 sources will be shown in a vertical stack of small tiles on the right
• Designate (click) a source to be the "main stream", it will be projected to the large tile
• Main stream will be projected to the designated audio/video mids as defined by the millicast track event
• You can change settings and view statistics for the main stream

Known issues

• Switching main stream multiple times will cause the former main stream to cut out. The reason for this is the source's mediastream's active property is changing from true to false. Unknown cause, is a blocking issue for the multisource milestone.

[vincentsong]

Please fix the CI with the help from @vishalkharge

[vishalkharge]

Please fix the CI with the help from @vishalkharge

@jackshen Tests are failing due to absence of the microphone/camera toggle buttons in the video view .

[vincentsong]

@vishalkharge could you please help @jackshen regarding the e2e test in CI? The test for Publisher App should work as before since we didn't change the publisher app code.