Rework user table

[mrjvs]

Changes:

• Replace Settings entity with two tables: users and user_settings. Removed Settings
• Move the follower system from Content entity to a dedicated user_follows table. Removed Content
• Update all miiverse-api follower code to use the new table
• Update all miiverse-api code to use the new user tables
• Update metrics to use the new tables instead of the old ones

Notes:

• Olive API has had some slight changes:
  • Having user content is no longer a requirement, only requires a User table where it checks for it
  • Follower logic has changed, it seems it was bugged but it needs some verifying
• There are a couple of broken followers, the data migration simply skips them. Otherwise you get foreign key constraint errors.
• For next PR: Update ban system so it's a dedicated table with history and not one field on the User

Testing:

• Test miiverse functionality

Part of #15
Fixes #73

[mrjvs]

After review, don't merge yet. A release is queued.