52 chist id from integer to uuid

This PR updates `Chist#id` type. It also refactors tests setup.
We should declare the `id` field as of type UUID.
[Postgres supports UUID](http://www.postgresql.org/docs/9.1/static/datatype-uuid.html) as a column type and Sequel handles it properly in the backend even though it will return you strings via the postgres adapter.