Mobile: add reset zoom button if zoom on GUI

Especially when using mobile phones, it accidentally can happen that one zooms in on the GUI elements and shifts the screen to the map, so that the GUI is not available anymore and you also cannot zoom out anymore.

Suggestion: add a "reset zoom" button in the lower right corner of the screen if a zoom is detected on the GUI. Problem: need a way to distinguish it from "rest zoom on map"

Reproduce by trying to zoom in on the search bar, then move the screen (not the map) so that only the map is on the screen -> zoom out of the GUI not possible anymore, because the zoom applies to the map.

Normal ORS, but also HEAL

Reproduce the problem on a mobile phone by zooming into the search bar and moving the screen until only the map remains. Start by tracing the GUI and map zoom handling, especially the lower-right controls; done means a reset-zoom control appears for GUI zoom and remains distinguishable from resetting map zoom in both normal ORS and HEAL.

Written by the indexing model from the issue text.