getData
    getData(params)
  
  Retrieves raw instance data given the url settings.
If url.getData is a function, that function will be called.  If url.getData is a
string, a request to that string will be made. If url is a string, a GET request is made to
url+"/"+IDPROP.
Parameters
- params 
{Object}:A object that represents the set of data needed to be loaded.
 
Returns
 {Promise<Object>}: 
A promise that resolves to the instance data.