Fix order of systems for new games

[fabio-t]

1. StartScreen should see map and bootstrap essentially doing nothing yet
2. If new game, load map generation; only process MapSystem when map is chosen (make the "init" a method that must be called, so we manually call it either in MapScreen or in StartScreen if player chooses Continue); only process "bootstrap" when player stats are chosen (again, should not actually process but just present an API to place creatures and trees), then enter playscreen

[fabio-t]

Right now Bootstrap runs before map, and thus object placement is wrong.