Move game logic plugin configuration to game-specific plugin

src/game/mod.rs

@@ -1,5 +1,13 @@
 mod objects;
+mod plugin;
 mod rng;
-pub mod runtime;
-pub mod seed;
-pub mod setup;
+mod runtime;
+mod seed;
+mod setup;
+pub mod state;
+
+#[allow(unused_imports)]
+pub mod prelude {
+    pub use super::plugin::{DataSource, GamePlugin};
+    pub use super::seed::Seed;
+}