feat: Extended call graph

[fabiomadge]

This PR extends the call graph with calls to other modules, thus removing the need for InterModularCallGraph. It also add a new print mode targeting the dot format for call graphs accessed with /dotCallGraph.

module Client { 
  import Util
  import Math // below Util

  function X(x: int): int { 0 }

  function Z(x: int): int { Math.Sqrt(X(x)) }

  class C extends Util.T {
    function Process(x: int): int {
      Z(x)
    }

    function Y(i: int): int {
      this.Process(i)
    }
  }
}
module Util {
  trait {:termination false} T {
    function Process(x: int): int 
  }
}
module Math {
  function Sqrt(x: int): int
}