Add support for multiple simultaneous meetings

[robcortez]

Problem

Currently, joining multiple meetings at once will cause sporadic behavior with the extension.

• If mute status is different in each meeting, browser icon will rapid change between muted and unmuted colors.
• Toggling mute status using browser button or hotkey will toggle mute in all joined meetings.

Solution

Add popup UI to browser action that will display a list of joined meetings and allow you to toggle by clicking icon next to meeting or via keyboard shortcut.

Need to come up with good UI element to differentiate between your joined meetings.
Possibilities:

• number of people in meeting
• meeting name
• meeting ID
• sort by time joined