Voice messages

Server

• Send 'message read' push notifications.
• Send a push to channel subscribers when channel is deleted
• API version updated to 0.19, minimum version to 0.17.
• Dependencies updates
• Docker file and drafty spec updated
• Bug fixes

The full list of changes: v0.18.7...v0.19.0

Voice messages and other UI/UX improvements in clients:

• iOS v1.9.0
• Android v0.19.0
• Webapp v0.19.0
• JS-SDK v0.19.0

Monitoring Exporter

• Exporter rebuilt with dependencies updated.