Predictoor support

[alexcos20]

For this epic "[Predictoor BE] Ship MVP" -- Add DT3 to subgraph repo

Changes in this PR:

• [A] Create schema
• [A] Update subgraph template
• [A] Create handlers in mappings
• Only merge when: we've deployed ocean contracts v2 to all networks, including Sapphire testnet

"Add tests" has been moved to -> #697

Example query:

query {
  predictContracts{
    id	
    token{
      name
    }
    blocksPerEpoch
    blocksPerSubscription
    truevalSubmitTimeoutBlock
    block
    eventIndex
    slots{
      id
      predictions{
        id
        user {
          id
        }
        stake
        payout {
          id
          predictedValue
          trueValue
          payout
        }
      }
      trueValues{
        trueValue
        floatValue
        txId
      }
      revenue
      revenues{
        
        amount
        txId
      }
      
      
    }
    subscriptions{
      
      user {
        id
      }
      expireTime
      txId
    }
    }
    
 }