Follow logic is backwards #130

For rewriting when this API is merged into core...

Follow's API is of the format /api/v2/users/:uid/follow where :uid is the person to follow, and _uid (or the uid from the non-master key) is the person whose edit list we are editing.

• This does not follow the convention of assuming that :uid is always referring to the subject.
• This also does not allow for situations where an admin with a non-master token wants to edit a user's follow list (the API will always only allow them to edit their own list

The API should be: /api/v2/users/:uid/follow/:targetUid where:

• _uid is the calling user (for permissions checking and so on)
• uid is the user whose follow list you are editing
• targetUid is the user you are (un)following