[ALOY-467] idAttribute assignable from Model config

The Backbone idAttribute property, which determines which backend property is the unique identifier for a Backbone model, should be assignable through the model.js config.definition object. That way Alloy can automatically apply that idAttribute to all created models. It will also signal Alloy to *_not_* create an additional "id" field like it does now for uniquely identifying records. Alloy should only create an additional id row if absolutely necessary and this will allow the developers to prevent that.

sample

This sample will tell Alloy (and Backbone) to use *myId* as the idAttribute for all models created from this definition. It will additionally tell Alloy to *_not_* create an additional id field for uniquely identifying records. If we were to remove the *idAttribute* property, then Alloy would in fact create an id column.

exports.definition = {
	config: {
		"columns": {
			"name":"TEXT",
			"nickname":"TEXT",
			"myId": "INTEGER PRIMARY KEY AUTOINCREMENT"
		},
		"adapter": {
			"type": "sql",
			"collection_name": "fighters",
		},
		"idAttribute": "myId"
	}
}