Spawn command

[ipiepiepie]

Sometimes newcomers on MelonBTA miss spawn due to the game spawn logic, which spawns player in the area, not a specific point.

ChunkCoordinates chunkcoordinates = world.getSpawnPoint();
int i = chunkcoordinates.x;
int j = chunkcoordinates.z;
int k = chunkcoordinates.y;
if (!world.worldType.hasCeiling()) {  // <-- here minecraft rolls random spawn coordinates
    i += this.random.nextInt(20) - 10;
    k = world.findTopSolidBlock(i, j);
    j += this.random.nextInt(20) - 10;
}

This PR fixes spawn issue by changing this logic. If spawn is set by /spawn set command, then server will always spawn new players and respawn players without bed on the exact spawn location.

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Also usage of /spawn is more intuitive for newcomers, because most minecraft servers are using /spawn command instead of /warp tp spawn, which currently used on MelonBTA.