The launcher lists San Vansterdam, the game's other maps and the custom maps of the mods that
load (start_maps.h), keeps the choice with its settings and starts the game in it, as its -map
does: a "load" at the front of the startup commands. A map no longer listed when the world can
load it (a map mod switched off or left out of the merge) is dropped after 20 s, and the game stays
in San Vansterdam. A launcher kept open no longer adds a launch's map to the last one's commands.
Tests: Launcher/Test/start_maps_tests.cpp.
