Move some user data into separate table(s)

The following discussion from !2623 (merged) should be addressed:

• @yorickpeterse commented on a discussion: (+3 comments)

  My main concern here is that our users table is already fairly wide. I'm wondering if it might not be a better idea to store these settings in some sort of user_settings and user_statistics (for the timestamps and such) tables. This would make updates on users more efficient, though it would also require more code. Perhaps it's best if we schedule that for 10.0 so we can also move over other columns?

changed milestone to %10.0

changed milestone to %Backlog

I'm thinking user_metadata might be better name than user_statistics. The idea of the two tables would be to make us end up with the following setup:

• users: contains the basic user details we need in most cases such as the username, password, Email address, state, etc
• user_metadata: contains timestamps for the last login, last updated at, created at, etc
• user_settings: contains details such as the Twitter handle, biography, can_create_group, can_create_team, the avatar, etc

The exact distribution may change, but the idea is that users only contains the crucial data we need on every page, while non critical data lives elsewhere. This makes writes faster, we put less vacuuming pressure on the DB, and we have greater control over what data we retrieve for the various pages.

mentioned in commit 595fc4d9