Continue Contribution contract and JS wrapper

lib/kredits.js

@@ -5,6 +5,7 @@ const Preflight = require('./utils/preflight');
 
 const ABIS = {
   Contributors: require('./abis/Contributors.json'),
+  Contribution: require('./abis/Contribution.json'),
   Operator: require('./abis/Operator.json'),
   Registry: require('./abis/Registry.json'),
   Token: require('./abis/Token.json')
@@ -76,6 +77,10 @@ class Kredits {
     return this.contractFor('token');
   }
 
+  get Contribution() {
+    return this.contractFor('contribution');
+  }
+
   // Should be private
   contractFor(name) {
     if (this.contracts[name]) {