Update @mozilla-protocol/assets to 3.0.0

[stephaniehobson]

This will:

• Bring in the new logos for Browser, Beta, Dev Ed, and Nightly.
• Bring in logos for Monitor, Send, and Lockwise.
• Bring in the new icon designs added in New icons protocol-assets#22
  • Note: this is a breaking change as:
    • the ui folder is removed and those assets moved one level up
    • the social icons are now in icons/social
    • the Focus logo has been removed
    • all the logo files have moved and have new names