FuelClient support range-based for-loops

[osrf-migration]

Original report (archived issue) by Shane Loretz (Bitbucket: Shane Loretz, GitHub: sloretz).

---

Currently FuelClient::Models(...) returns an instance ModelIter. Iterating over all models looks like

auto iter = client.Models(server);
for (; iter; ++iter)
{
  Model & model = *iter;
  // ...
}

It would be more convenient to use range based for loops

for (Model & model : client.Models(server))
{
  // ...
}

This can be done by making a function return an object with special methods begin() and end() where begin returns what FuelClient::Models(...) returns now, and end returns an iterator that compares inequal to a valid iterator.

class Models
{
    /// \brief special method to support range-based for-loops; must be lowercase
   public: ModelIter begin();

    /// \brief special method to support range-based for-loops; must be lowercase
   public: ModelIter end();
}

Since fuel-tools has already been released and a function's return type is not part of its signature, tick-tocking this requires changing the name of the function on FuelClient.

     /// old and busted
     public: IGN_DEPRECATED(2) ModelIter Models(const ServerConfig &_server);

     /// new hotness
     public: Models QueryModels(const ServerConfig &_server);