Block->ommers: resolve into EthqlBlocks

[raulk]

Support the following:

{
  block(number: 5000000) {
    ommers {
      hash
      transactionCount
      transactions {
        hash
      }
    } 
  }
}

Make sure that the transactionFilter and the block fetch hints (log and transactions) work properly.

[akhila-raju]

Ommers won't have transactions, correct? See example ommer.