Validate contribution docs against schema

Currently requires an open PR branch for the schemas, which is adding
date and time for contributions.

refs #30

lib/contracts/contribution.js

@@ -1,5 +1,20 @@
 const ethers = require('ethers');
 
+const schemas = require('kosmos-schemas');
+const tv4 = require('tv4');
+const validator = tv4.freshApi();
+
+validator.addFormat({
+  'date': function(value) {
+    const dateRegexp = /^[0-9]{4,}-[0-9]{2}-[0-9]{2}$/;
+    return dateRegexp.test(value) ? null : "A valid ISO 8601 full-date string is expected";
+  },
+  'time': function(value) {
+    const timeRegexp = /^([01][0-9]|2[0-3]):([0-5][0-9]):([0-5][0-9]|60)(\.[0-9]+)?(([Zz])|([\+|\-]([01][0-9]|2[0-3]):[0-5][0-9]))$/;
+    return timeRegexp.test(value) ? null : "A valid ISO 8601 full-time string is expected";
+  }
+})
+
 const ContributionSerializer = require('../serializers/contribution');
 const Base = require('./base');
 
@@ -48,12 +63,15 @@ class Contribution extends Base {
   }
 
   addContribution(contributionAttr, callOptions = {}) {
-    let json = ContributionSerializer.serialize(contributionAttr);
-    // TODO: validate against schema
+    let jsonStr = ContributionSerializer.serialize(contributionAttr);
+
+    // Validate JSON document against schema
+    let result = validator.validate(JSON.parse(jsonStr), schemas['contribution']);
+    if (!result) { return Promise.reject(validator.error); }
 
     return this.ipfs
-      .add(json)
-      .then((ipfsHashAttr) => {
+      .add(jsonStr)
+      .then(ipfsHashAttr => {
         let contribution = [
           contributionAttr.amount,
           contributionAttr.contributorId,