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/serializers/contribution.js

@@ -14,6 +14,8 @@ class Contribution {
   */
   static deserialize(serialized) {
     let {
+      date,
+      time,
       kind,
       description,
       details,
@@ -21,6 +23,8 @@ class Contribution {
     } = JSON.parse(serialized.toString('utf8'));
 
     return {
+      date,
+      time,
       kind,
       description,
       details,
@@ -38,6 +42,8 @@ class Contribution {
   static serialize(deserialized) {
     let {
       contributorIpfsHash,
+      date,
+      time,
       kind,
       description,
       url,
@@ -50,6 +56,8 @@ class Contribution {
       "contributor": {
         "ipfs": contributorIpfsHash
       },
+      date,
+      time,
       kind,
       description,
       "details": details || {}