[part 3] Port follower and current user datasource to miiverse-api

[mrjvs]

Changes:

• Added follower/unfollow endpoints, also implemented into frontend codebase
• Added follower/following listing endpoints, also implemented into frontend codebase
• Added endpoint to list a users posts, also implemented into frontend codebase
• Added endpoint to get the current user:
  • It does not error when banned, since it's used to get current account status as well
  • It's requested every frontend page and is the current auth state of the request
  • It does a few miscellaneous tasks: update mii name, set last_active, clear ban if date has passed
  • It's the replacement for getting the current user settings and current user content
• Updated the guest guard, it now ignores bans as well. The user guard now checks it

Notes:

• Depends on [part 2] Port activityfeeds datasource to miiverse-api #480 - dont merge until that PR is merged

Resolves a part of #112

[ashquarky]

LGTM

[mrjvs]

Gonna wait for #494 before merging, otherwise we have another suite of tests to run before it