Split 0x.js into contract-wrappers, order-watcher but keep 0x.js as a unifying library with the same interface

packages/contract-wrappers/test/utils/constants.ts

@@ -0,0 +1,9 @@
+export const constants = {
+    NULL_ADDRESS: '0x0000000000000000000000000000000000000000',
+    ROPSTEN_NETWORK_ID: 3,
+    KOVAN_NETWORK_ID: 42,
+    TESTRPC_NETWORK_ID: 50,
+    KOVAN_RPC_URL: 'https://kovan.infura.io/',
+    ROPSTEN_RPC_URL: 'https://ropsten.infura.io/',
+    ZRX_DECIMALS: 18,
+};