Add new `AllVotesQuery` object.

This will replace `IVoteRepository.GetAllVotes()`.
Add `AllVotesQuery` to `SessionController`.
Use the new query object in `SessionController`.
Fix namespace in `ConferenceBuilder` tests.
Remove `VoteRepository` from `SessionController`.
Replace `VotesRepository` with new query object.

Update the `DataProvider` and its factory to use the new `AllVotesQuery`
object rather than the `VotesRepository`.