feat(track): all of the unevenness in one attribute, with values for each path of a switch

Usage, before endtrack, in mm, 0-100, separated by semicolons with no
spaces:

  a plain track:  uneven value;up;side;cross;dip
  a switch:       uneven p1-p2;p3-p4;up p1-p2;side p1-p2;up p3-p4;side p3-p4

  uneven 18           the value alone
  uneven 18;;;25;6    with its own cross level and dip at the joints
  uneven 0;;30        sideways alone
  uneven 14;35        a switch, 14 on the straight path, 35 on the diverging

What's left out takes the first number, the dip goes by the up and down
one, and a path p3-p4 with no numbers of its own takes those of p1-p2.
This replaces unevenup, unevenside, unevencross and jointdip. The fields
in the editor stay, track panel, section Ride and sound.

At the end they share, the paths of a switch keep to the lower value, and
each comes to its own value along the way. Joined switches take the lowest
of the same path, a path joined to another path the lower of the two, and
a plain track comes to the value of the path it meets. See
track_uneven_doc.md.

editor/editorTrack.hpp

@@ -59,6 +59,9 @@ class editor_track
 		float unevenup{-1.f};
 		float unevenside{-1.f};
 		float unevencross{-1.f};
+		float unevenbranch{-1.f};
+		float unevenbranchup{-1.f};
+		float unevenbranchside{-1.f};
 		float jointdip{-1.f};
 		bool sleepers{false};
 		float sleeper_frequency{0.6f};