Add Event trigger loop

[Lleutch]

Currently we do not support features such as triggers, which allow to have UI only modification depending on certain state of UI related element (a trigger on the background color of a button when we hover over it.)

With MVU, to do that we would need to go through the whole MVU event loop which might take a bit of time, but also this means that we should account that new button state (onHover) inside the Model, which pollutes the Model with unecessary/useless information.