Fix bootstrapping of mvp-sample after update to spring-vaadin-mvp

A summary of what's been updated

* All component listeners are @UIScope annotated
* Presenter sub-classes that are @VaadinPresenter annotated are now @UIScope, per https://github.com/peholmst/vaadin4spring/pull/79
* Remove @Push on UI and Maven dependency on vaadin-push; not being used