Remove ethcore::common re-export module (#2792)

* no longer export action_params

* remove transaction, header, receipt re-rexports from common

* remove env_info and builtins re-exports from common

* remove everything but util export from common

* replace common usages with util, remove module

* add a prelude module for ethcore-bigint

ethcore/src/json_tests/transaction.rs

@@ -18,6 +18,7 @@ use super::test_common::*;
 use evm;
 use ethjson;
 use rlp::{UntrustedRlp, View};
+use transaction::{Action, SignedTransaction};
 
 fn do_json_test(json_data: &[u8]) -> Vec<String> {
 	let tests = ethjson::transaction::Test::load(json_data).unwrap();