Add more info to announced components in Discovery Server

[romeovs]

This is a feature request for the Discovery Server.

See https://github.com/TheThingsIndustries/console/issues/381

It would be nice if we can add extra information to an announcement. We should add:

• an Emoji or IconURL field
• an Operator field, with information about the operator (name, homepage, ...)

[johanstokking]

Also contact uri (maybe link-like, so mailto: or https://)

[htdvisser]

Moving this to v3. We'll have to come up with a different mechanism, considering that there likely won't be a discovery server in v3...