Proper UI appearance for UI Prefab

[cai-mobfish]

Detail

Currently, the UI is pure button with text. We need icon so that the default UI Prefab is directly usable.

We need following UI Elements:

• Cardboard icon for switching vr view
• QR code scan icon
• split line at the middle bottom of the screen
• Cancel or back button on top left side

[cai-mobfish]

These will be how it looks like default. Dev teams can modify it as they see fit.