Add very initial version of smart contracts with tests

contracts/helpers/Migrations.sol

@@ -0,0 +1,23 @@
+pragma solidity ^0.6.0;
+
+contract Migrations {
+  address public owner;
+  uint public last_completed_migration;
+
+  constructor() public {
+    owner = msg.sender;
+  }
+
+  modifier restricted() {
+    if (msg.sender == owner) _;
+  }
+
+  function setCompleted(uint completed) public restricted {
+    last_completed_migration = completed;
+  }
+
+  function upgrade(address new_address) public restricted {
+    Migrations upgraded = Migrations(new_address);
+    upgraded.setCompleted(last_completed_migration);
+  }
+}