Add support for data preparation with promises on save

[andreybs11]

We currently support only data preparation through a callback function pass by parameters to the save data binder.

this.saveDataBehavior = new SaveDataBinder({
component : this,
saveProxyCallback : $.proxy(proxy.save, proxy),
prepareDataToSave : this._prepareDataForRequest,
onComponentSaveSuccess : $.proxy(this._onSaveSuccess, this),
onComponentSaveError : $.noop
});

Certain scenarios may require a data preparation with promises like: third party services requesting a token/approval...