blockchain split into few separate submodules, cleanup insert_block process

ethcore/src/blockchain/mod.rs

@@ -0,0 +1,10 @@
+pub mod blockchain;
+mod best_block;
+mod block_info;
+mod bloom_indexer;
+mod cache;
+mod tree_route;
+
+pub use self::blockchain::{BlockProvider, BlockChain};
+pub use self::cache::CacheSize;
+pub use self::tree_route::TreeRoute;