This allows for the discourse automation plugin to have a "Send Slack
Message" script.
The script fields are a message, url, and slack channel. This will allow
for a custom slack message to be posted but can link back to an
arbitrary url (hopefully a discourse url) like a list of unanswered
topics instead of strictly only allowing a slack message that links back
to a Discourse Post object.
Once configured, this adds a new item to the context menu of slack messages. When clicked, the menu item will generate a transcript and present the user with a custom "Post to Discourse" modal. This provides the same functionality as the existing slash-command interface, but is much more user friendly.
- Stop using `break` in a block - it doesn't work. The failure here was hidden because it was within a `defer` block, so would not cause a server error
- Refactor the error handling so that the error is passed back to Slack and displayed to the user
- Return specific error messages for user / message-history / message errors
- Tidy up the SlackCommandController to make all non-requestable methods private
- Add a test to ensure error messages are passed correctly to Slack
