[DISCUSSION] Clean up the domain cruft

[mrchrisadams]

The database the provider portal runs on is much older than the django codebase it now runs on.

As a result, we have a bunch of confusing columns in the database, and references to concepts that don't make so much sense now.

This issue exists to collect them, so we can tidy them up at opportune times in future.

[mrchrisadams]

Hosting provider model :showonwebsite and our directory

showonwebsite refers to whether a given provider appears in our directory, at /directory. This can be a tad confusing, as you can have a provider that shows as green in checks but does not appear in the directory.