Editor: rebuild the plan library around a solved document, and bend turnouts onto curves

The library was a heap of half-built services - fitting, parallelism, niwelety,
an SVG writer - that never met each other. In their place is one authored
Document and one solver that lays it whole: tracks as element chains, turnouts
placed on them, and a Solution that is rebuilt from scratch every time and never
fed back into the document. What cannot be laid comes back as a diagnostic with
the number in it rather than as silence or a fitted-away error.

Turnouts are dimensioned the way the drawings dimension them. The blade follows
Koc's rys. 5.9 - the curve is theoretically tangent to the opornica at PR, the
blade starts at a with a planed nose of d, and A is where the rail stands u
thick - and a + d derived that way lands on his tablica 5.1. Bending follows
5.3.6: it rotates the triangle OBC about the centre of the turnout, so the
tangent t and the crossing angle stand and both radii follow from them. That is
Koc's (5.7) and (5.8) without coding either, and it puts a symmetrically bent
Rz 49E1-190-1:9 on the catalogue's Rlus 49E1-380,292-1:9. A rozjazd standing on
a curve is bent onto it; one on a track drawn straight can carry a bend of its
own. The szyny laczace take up the difference, because the switch and the frog
are only bent, not re-cut.

The plan panel draws all of it: the catalogue drawing of a type with its
construction points, the theoretical arc dashed where no rail runs, and the
blade nose as the straight it is cut as. Dragging a straight now stops where it
would pull the track out from under a turnout.

File format goes to m0s 6. Versions 3 to 5 still open.

CMakeLists.txt

@@ -513,6 +513,13 @@ endif()
 find_package(Threads REQUIRED)
 target_link_libraries(${PROJECT_NAME} Threads::Threads)
 
+# the editor's map imagery talks to a WMS over https. windows has WinHttp in the platform sdk;
+# everywhere else libcurl is the transport (see editor/orthophoto.cpp)
+if (NOT WIN32)
+	find_package(CURL REQUIRED)
+	target_link_libraries(${PROJECT_NAME} CURL::libcurl)
+endif()
+
 find_package(GLM REQUIRED)
 target_include_directories(${PROJECT_NAME} PRIVATE ${GLM_INCLUDE_DIR})