Improve Slack message formatting

[amitfrid]

Improve Slack message formatting with links, fields with label-value pairs, etc. Currently the plain text messages look sub-optimal, especially in device list etc.

[amitfrid]

Would be nice if the device list was sorted alphabetically.

[amitfrid]

FYI, Slack really only allows plain text messages. It will make hyperlinks clickable though so we could include those.

[alecthegeek]

Are you sure? this says you can use a subset of markdown.

https://api.slack.com/docs/message-formatting#message_formatting