Optimize chunk sets requested by players

[OLEGSHA]

Currently, chunks are loaded in an ellipsoid around the player. This is wasteful: many of the requested chunks are empty or invisible. Instead, the player should not request these chunks.

The relevant code is in ru.windcorp.progressia.server.Player.requestChunksToLoad(Consumer<Vec3i>).

The solution entails three parts:

• Make client and server agree on what block faces are opaque by moving opacity-related methods from interfaces in ChunkRenderOptimizerSurface into BlockData and TileData
• Add similar opacity methods to entire chunks that determine whether chunk walls are entirely opaque
• Change request algorithm to ignore chunks that are empty or hidden by opaque chunk walls

Although this is up for debate, a reasonable algorithm for step 3 may be

request 3x3x3 cube around player;
iterate chunks around player with flood-fill algorithm:
    start at player location;
    do not pass through opaque chunk walls;
    do not go further than load-distance away from start;
    if a chunk is not empty, request it.