Create model collection plugin

This PR implements the `can.Model.Collection` plugin.

`can.Model.Collection` combines params and list of items under one class which does two things:

1. It reduces the amount of code needed to wire up filterable and sortable `findAll` requests
2. It removes code related to the data loading from the controllers

Without the `can.Model.Collection` plugin, code would look like this:

    var ImagesControl = can.Control({
      init : function(){
        this.options.params = new can.Observe;
        this.on();
        this.imagesList = new can.Observe.List
    
        this.element.html(someView({
          imagesList : this.imagesList
        }))
    
        this.loadData()
      },
      'a click' : function(el, ev){
        this.options.params.attr('foo', 'bar');
      },
      "{params} change" : 'loadData',
      loadData : function(){
        ImageModel.findAll(this.options.params.serialize(), this.proxy('updateData'));
      },
      updateData : function(data){
        this.imagesList.replace(data);
      }
    })

`can.Model.Collection` shortens it to this:

    var ImagesControl = can.Control({
      init : function(){
        this.imageCollection = new ImageModel.Colle;tion:
    
        this.element.html(someView({
          imagesList : this.imageCollection.list
        }))
    
        this.imageCollection.load();
      },
      'a click' : function(el, ev){
        this.imageCollection.params.attr('foo', 'bar');
      }
    })