Georeference a new map against a point in Poland

"New map" now asks what is being started. A fictional scenery keeps its own
frame, where coordinates mean nothing outside it. A real one pins the
scenery's zero to a point picked off a map of Poland, so the plan is drawn
in EPSG:2180 - the frame the layout library already works in, and the one
Geoportal serves imagery in.

The projection is the standard transverse Mercator series for PUWG 1992 on
GRS80. Checked against known values: the central meridian comes out at
easting 500000 exactly, Warszawa at 637382/486757, Krakow at 567614/244588,
Gdansk at 477038/720937.

The map behind the picker is a schematic border outline plus the larger
cities, projected from geographic coordinates on first use. It is coarse on
purpose - it is there to point at a region, not to measure against - and the
dialog says so. No network is involved.

utilities/Globals.h

@@ -82,6 +82,10 @@ struct global_settings {
     // rzut z góry bez perspektywy, do kreślenia planu torowiska na tle wczytanej scenerii
     bool editor_ortho{ false };
     float editor_ortho_extent{ 250.f }; // połowa wysokości widoku w metrach, czyli zoom rzutu
+    // punkt EPSG:2180 odpowiadający zeru scenerii. Bez tego sceneria jest fikcyjna i jej współrzędne
+    // nie znaczą nic poza nią samą
+    bool scenery_georeferenced{ false };
+    glm::dvec2 scenery_origin{ 0.0, 0.0 };
     std::string local_start_vehicle{ "EU07-424" };
     int iConvertModels{ 0 }; // tworzenie plików binarnych
     int iConvertIndexRange{ 1000 }; // range of duplicate vertex scan