add custom class to notify

[lc-thomasberger]

Notify should accept custom classes

Since Notify accepts now a custom view, it will need better styling support. For instance HotGraphic will need to reset the background-color of the popup. This will only work if a class can be set at the top level of Notify.

            Adapt.trigger("notify:popup", {
                _view: new HotgraphicPopupView({
                    model: this.model
                }),
                _isCancellable: false,
                _classes: ' hotgraphic' // will be added tho notfiyView.$el
            });

[lc-thomasberger]

_isCancellable hides the close button and also disables close by clicking on the backdrop.
I think it would be good to have more fine grained options here:
_showCloseButton
_closeOnBackdrop

_isCancellable would set both values for backwards compatibility.

[oliverfoster]

could you split _isCancellable out before we document the subview stuff? @lc-thomasberger
now is the time to do that.