Add to Ratel a field of total number of nodes | Feature, has References.

[MichelDiz]

References: hypermodeinc/dgraph#1619

Can serve as statistics in Ratel.

In the Schema field put an option to request the total nodes for that predicate. It updates as the user clicks to request each one. Ratel would generate a query like the one below.

e.g:

{
  total (func: has (director.film) ) {
    count(uid)
  }
} 

[paulftw]

Data explorer does that ATM, slowly. Better fetch is blocked on the "has()" optimization. Will be fixed once we migrate play to 1.0.10.