Update UI and add Proactive Video feature to Websocket-demo-app

[tpareek18]

Description

Introducing the following changes to the gemini/multimodal-live-api/websocket-demo-app:

• Cleaner and more-organized UI for the Websocket Demo Application
• Added functionality to allow for client-side configuration to enable proactive video in a session
• Added functionality to allow for client-side control of audio and video sampling rate
• Minor fixes for microphone and video toggle functionality

[holtskinner]

Assigning to @ZackAkil as he originally created this