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/test_common.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
-pub use common::*;
+pub use util::*;
 
 macro_rules! test {
 	($name: expr) => {