cmd/geth, cmd/utils, core, rpc: renamed to blockchain

* Renamed ChainManager to BlockChain
* Checkpointing is no longer required and never really properly worked
when the state was corrupted.

core/manager.go

@@ -26,7 +26,7 @@ import (
 type Backend interface {
 	AccountManager() *accounts.Manager
 	BlockProcessor() *BlockProcessor
-	ChainManager() *ChainManager
+	BlockChain() *BlockChain
 	TxPool() *TxPool
 	ChainDb() ethdb.Database
 	DappDb() ethdb.Database