Publisher-to-subscriber and vice-versa

Summary:

• Added Permissions section in the user options dropdown
• Use proper event system to handle audio/video status indication
• Add "Nickname" item to the participant options menu
• Code improvements

Test Plan: ./phpunit

Reviewers: #hkccp_developers

Subscribers: #hkccp_developers

Differential Revision: https://git.kolab.org/D2149