Global stats

[mihaisc]

Fixes #316

example

{
  globalStatistic(id:"1"){
    id
    orderCount
    nftCount
    datatokenCount
    poolCount
    fixedCount
    dispenserCount
    totalPoolSwapVolume{
      id
      token {
        id
        symbol
      }
      value
    }
    totalLiquidity{
      id
      token {
        id
        symbol
      }
      value
    }
    totalFixedSwapVolume{
      id
      token {
        id
        symbol
      }
      value
    }
}
}