Editor parts:
- correctly update the dirty state on undo/redo
- read dilution of precision data and add warnings
- add undo/redo buttons
- make the coordinates of the images editable
- disable closing while a thread is running
- save the column ordering
- sorting of the images
- fix scroll-wheel interaction of the tabs
- when resizing the widget horizontally, the star moves back and forth
- add a tab for forward-geocoding

GeoIface parts:
- control over clustering grid size (UI)
- re-cluster only every few pixels of panning
- the clustering model does not go deep enough - when zooming in on Marble OSM, the positions are quantized
- snapping for drag-and-drop coming in from outside the map
- snapping in the Google Maps backend
