Add proposal form

Closes #6

Form can be prefilled using query params on the route. The params are
`recipient`, `amount`, `url` and `ipfsHash`.

tests/unit/controllers/proposals/new-test.js

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