feat: Upload floor plan image: scale/translate marker positions

[resah]

When uploading a new floor plan background image with already existing markers, there might be the case, that the image size and/or aspect ratio changed and the marker positions do not match anymore.
To allow adjusting marker positions

• marker positions should be scalable and translatable
• new marker positions should be previewed directly in map

The adjustments are automatically applied to all markers when new floor plan image is stored.

To simplify usage, it would be nice to

• allow linking/unlinking value pairs
• provide a button to reset values (per value pair)

Suggestion