Display related tools in the User show API.

:fork_and_knife: 

This includes the tools that user owns and the tools they collaborate on.

For example: `curl http://localhost:3000/api/v1/users/supermarket` returns:

``` json
"tools": {
  "owns": {
    "berks": "http://localhost:3000/api/v1/tools/berks",
    "knife": "http://localhost:3000/api/v1/tools/knife"
  },
  "collaborates": {}
}
```

Trello card: https://trello.com/c/SQtSHidB