add sorting to kendo.Backbone.DataSource

[mxriverlynn]

Need to look in to basic sorting capabilities for the kendo.Backbone.DataSource and what implications this has.

At a minimum, should support sorting the in-memory Backbone.Collection. Probably needs to do it using Backbone's standard sorting features... perhaps through a proxy/decorator to keep the original models / collection clean of KendoUI's code for this.