Create slider/carousel modal for multipage messages

[ivokwee]

Request a slider/carousel inside a modal window like below. With perhaps image on top and multi page scrolling. This would be good for a "What's new" or multiple message at startup. Often app have this. New features could be announced (this was one suggestion from a user, because they would like to know the new features). We have hidden new features in the user profile but I guess no one saw that.

As starter, the welcome page has a carousel from boostrap. See components/ui/bs-components.R for the code.