Replace JpaRepository with PagingAndSortingRepository

As recommended by Ollie, alter the repository so it's not JPA specific. This had a ripple effect of replacing List<Todo> with Iterable<Todo>.

See: http://stackoverflow.com/questions/14014086/what-is-difference-between-crudrepository-and-jparepository-interfaces-in-spring
Merge pull request #3 from gregturn/master

Replace JpaRepository with PagingAndSortingRepository