Add the ability to respawn and improve controller port mapping (#72)

Reviewed-on: #72
Co-authored-by: Álex Román Núñez <eirexe@eirteam.moe>

src/player.rs

@@ -10,5 +10,8 @@ use bevy_ggrs::prelude::*;
 #[derive(Default, Component)]
 #[require(Rollback, Transform)]
 pub struct Player {
+    /// Dense GGRS session index.
     pub handle: usize,
+    /// Port used for port-dependent gameplay such as respawn placement.
+    pub controller_port: usize,
 }