Extract serializer logic into lib

To use the same code in hubot I extracted the serializer logic into lib to later move it into `truffle-kredits` when we are done with all other common logic.

tests/unit/lib/kredits/serializers/contributor-test.js

@@ -0,0 +1,53 @@
+import { module, test } from 'ember-qunit';
+import schemas from 'npm:kosmos-schemas';
+import tv4 from 'npm:tv4';
+import { ContributorSerializer } from 'kredits-web/lib/kredits';
+
+module('Serializers contributor');
+
+test('#serialize returns a valid JSON-LD representation', function(assert) {
+  let serialized = ContributorSerializer.serialize({
+    name: 'Satoshi Nakamoto',
+    kind: 'person',
+    github_uid: 123,
+    github_username: 'therealsatoshi',
+    wiki_username: 'Satoshi',
+  });
+
+  let valid = tv4.validate(JSON.parse(serialized), schemas['contributor']);
+  assert.ok(valid);
+});
+
+test('#deserialize returns a valid object representation', function(assert) {
+  let json = JSON.stringify({
+    "@context": "https://schema.kosmos.org",
+    "@type": "Contributor",
+    "kind": "person",
+    "name": "Satoshi Nakamoto",
+    "accounts": [
+      {
+        "site": "github.com",
+        "uid": 123,
+        "username": "therealsatoshi",
+        "url": "https://github.com/therealsatoshi"
+      },
+      {
+        "site": "wiki.kosmos.org",
+        "username": "Satoshi",
+        "url": "https://wiki.kosmos.org/User:Satoshi"
+      }
+    ]
+  });
+  let deserialized = ContributorSerializer.deserialize(json);
+
+  let expected = {
+    name: 'Satoshi Nakamoto',
+    kind: 'person',
+    github_uid: 123,
+    github_username: 'therealsatoshi',
+    wiki_username: 'Satoshi',
+    url: undefined,
+    ipfsData: json,
+  };
+  assert.deepEqual(expected, deserialized);
+});