core, core/state, trie: EIP158, reprice & skip empty account write

This commit implements EIP158 part 1, 2, 3 & 4

1. If an account is empty it's no longer written to the trie. An empty
  account is defined as (balance=0, nonce=0, storage=0, code=0).
2. Delete an empty account if it's touched
3. An empty account is redefined as either non-existent or empty.
4. Zero value calls and zero value suicides no longer consume the 25k
  reation costs.

params: moved core/config to params

Signed-off-by: Jeffrey Wilcke <jeffrey@ethereum.org>

light/state_test.go

@@ -41,7 +41,7 @@ func makeTestState() (common.Hash, ethdb.Database) {
 		st.AddBalance(addr, big.NewInt(int64(i)))
 		st.SetCode(addr, []byte{i, i, i})
 	}
-	root, _ := st.Commit()
+	root, _ := st.Commit(false)
 	return root, sdb
 }