Add IPFS service (#4)

Add IPFS service

Add the `ipfs-api` JS library and a service using the browserified
version of it. The service has functions for storing and reading file
contests.

tests/unit/services/ipfs-test.js

@@ -0,0 +1,12 @@
+import { moduleFor, test } from 'ember-qunit';
+
+moduleFor('service:ipfs', 'Unit | Service | ipfs', {
+  // Specify the other units that are required for this test.
+  // needs: ['service:foo']
+});
+
+// Replace this with your real tests.
+test('it exists', function(assert) {
+  let service = this.subject();
+  assert.ok(service);
+});