Major release, possible breakage ahead

This release change the implementation language of the adapter from Coffeescript to ES6 (thanks @HP41 !) therefore there might be some breakage. Please report any issues.

Changes

• Convert to ES6
• Use mattermost-client @ 5.0.0

• Add Websocket event user_role_updated

• Reconnect on team loading error
• non-TLS config fix

• Improved reconnect logic

• Proxy support
• Improve reconnect logic

• Improve v4 API support
• Various bug fixes

• Switch to using Mattermost v4 API

• Fix dependency

• Team name check is now case insensitive

• Fix Slack attachment posts