Avatars sent out of band, trusted badges, bug fixes

IMPORTANT: Requires database upgrade

Multiple new features:

• Trusted account and topic parameters which enable tagging account as verified, staff, etc.
• Support for sending links to avatars instead of binary data.
• More informative push notifications.
• Simplified message routing.
• Support for more SMTP authentications mechanisms.
• Binaries now include Apple M1 builds (mac-arm64), gox build dependency removed.
• Bug fixes.

The full list of changes: v0.17.10...v0.18.0

Client releases:

• iOS https://github.com/tinode/ios/releases/tag/v1.8.0
• Android https://github.com/tinode/tindroid/releases/tag/v0.18.0
• Web https://github.com/tinode/webapp/releases/tag/v0.18.0
• JS SDK https://github.com/tinode/tinode-js/releases/tag/v0.18.0