Allow users to self-classify by poster type

[emilyhunt]

Will be extremely helpful to many other things to know who's e.g. a science astronomer, astrophotographer, etc.

The rough idea for this will be:

• The bot has a thread of classification posts that users can like
• These likes are collated by the bot and added to the Account part of the database
• To detect people changing preferences, the posts will occasionally have to have all likes tallied again.

Would probably keep it simple, and ask people to put themselves into one or more of these categories:

• Research astronomer (whether or not currently employed)
• Astrophotographer
• Science communicator