Hide a page element

[tilmx]

As a user I want to have an option to hide a page element. The element should stay shown in the page element list, but hidden in the preview pane.

With this features, designers can try out different states (different elements hidden/shown) of a page without losing all the entered properties by deleting the element.

This features should be accessible via Context Menu (right-click on element) and an visual indication next to the element inside the element list (design tbd).

[marionebl]

Implemented by introduction of the builtin conditional component