add horizontal / collapsible level switcher

[smallTrogdor]

Description

Implement the horizontal and collapsible FloorSwitcher.

Motivation

The current floor switcher takes up a lot of space of the screen when not necessarily being needed. The new horizontal and collapsible floor switcher is much nicer.

Proposed Solution (optional)

Either:

• integrate it in the existent FloorSwitcher (with other constructor and set default)
• make a new FloorSwitcher

List Pros and Cons!