Graylog Plugin Slack Versions Save

1. Add back output message attachments (more information check box).
2. Add custom message support to output messages.
3. Convert custom messages to attachments to support color.
4. Update configuration dialog options.
5. Fix Slack image icon support (icon_url).

Various bug fixes. Links to alert source

Add custom templated message feature. Removed features that are now solved by templates.

• Added support for custom fields in alarm callback. Thanks @francescou and @aeke!

• Added summaries for alert messages. Thanks @robbanp!
• Added support for using a proxy server when accessing Slack (or Mattermost). Thanks @simonknoll!

This release enables the plugin to operate with Mattermost, tested and working. Thanks to @madchap and @EliotBerriot for their help!