Split Topics for P2P Beacon Chain and P2P Sharding

[terencechain]

Currently all the P2P topics are grouped under sharding and used by mapping topicTypeMapping in topics.go. This issue should separate beacon chain related topics out of sharding topics.

Under sharding/messages.proto:

// TODO: Split the topics into p2p for beacon chain and p2p for sharding.

enum Topic {
  UNKNOWN = 0;
  COLLATION_BODY_REQUEST = 1;
  COLLATION_BODY_RESPONSE = 2;
  TRANSACTIONS = 3;
  BEACON_BLOCK_HASH_ANNOUNCE = 4;
  BEACON_BLOCK_REQUEST = 5;
  BEACON_BLOCK_RESPONSE = 6;
  CRYSTALLIZED_STATE_HASH_ANNOUNCE = 7;
  CRYSTALLIZED_STATE_REQUEST = 8;
  CRYSTALLIZED_STATE_RESPONSE = 9;
  ACTIVE_STATE_HASH_ANNOUNCE = 10;
  ACTIVE_STATE_REQUEST = 11;
  ACTIVE_STATE_RESPONSE = 12;
}