Add buddies

https://trello.com/c/bjJNY4Ub/44-users-can-friend-each-other

Some latent code was commented for next PR
What about making a `pending` scope for `BuddyRelationship` that finds items that are not confirmed? Then you can do:

```ruby
BuddyRelationship.pending.where(user_id: id).pluck(:buddy_id)
```