Webpage help tour

Created by: Masboes

This adds a help button that starts a tour of the major elements on the page to explain to a new user how to use the website. The tour is incomplete, but extending it after new elements get added is trivial.

Above the definition of the current tour is briefly explained how a step in the tour is defined. Is consists of a message, an element selector like used in css, and an optional positioning attribute.

I also changed the upload button from a label to an actual button. This makes more sense in the tour, since we have 'app-screenshot-button > button' and 'app-visualization-picker > button' and now also 'app-upload-tool > button'