Constructors and contract creation (#11)

Implement constructor logic and support create/create2 in the mock runtime

Signed-off-by: xermicus <cyrill@parity.io>

crates/integration/contracts/flipper.sol

@@ -4,6 +4,10 @@ pragma solidity ^0.8;
 contract Flipper {
     bool coin;
 
+    constructor(bool _coin) {
+        coin = _coin;
+    }
+
     function flip() public {
         coin = !coin;
     }