convert SplitPayment to initializers

contracts/mocks/SplitPaymentMock.sol

@@ -0,0 +1,10 @@
+pragma solidity ^0.4.24;
+
+import "../Initializable.sol";
+import "../payment/SplitPayment.sol";
+
+contract SplitPaymentMock is Initializable, SplitPayment {
+  constructor(address[] payees, uint256[] shares) public {
+    SplitPayment.initialize(payees, shares);
+  }
+}