Import/Migrate existing kredits contracts

This brings in the current state of the kredits contracts incl. the
Contributors, Operator and Token contract.

migrations/1522427321_contributors.js

@@ -0,0 +1,13 @@
+var Registry = artifacts.require('./Registry.sol');
+var Contributors = artifacts.require('./Contributors.sol');
+
+module.exports = function(deployer) {
+  deployer.deploy(Contributors).then(function(contributors) {
+    console.log('Registry address: ', Registry.address);
+    console.log('Contributors address: ', Contributors.address);
+    Registry.deployed().then(function(registry) {
+      registry.addVersion('Contributors', Contributors.address);
+      registry.createProxy('Contributors', 1);
+    });
+  });
+};