support xrc20 transfers in xrc20 contract addresses

[ququzone]

we can use below graphql to query those transactions:

query {
  xrc20 {data: byContractAddress(address: "io19fsq8e9krrlng4ay5gyq6q5tqfym28yq9ly0fz", numPerPage: 10, page: 1) {
    exist
    xrc20 {
      contract
      hash
      timestamp 
      from        
      to        
      quantity        
      __typename     
    }      
    count     
    __typename    
  }    
    __typename  
  }
}

So at explorer XRC20 tab, we can first use this QL to query data, if returned data is empty then use origin QL.