Add youngest query parameter for Olympians endpoint

As a user,

I can submit a request to the endpoint `/api/v1/olympians` with a query parameter of `age=youngest` and receive the youngest Olympian in the system, formatted identically to the normal index.

Sample response:

``` JSON
{
[
{
"name": "Ana Iulia Dascl",
"team": "Romania",
"age": 13,
"sport": "Swimming"
"total_medals_won": 0
}
]
}
```