ENH: Set up ember-simple-auth (initial) (#12)

Fixes #6

app/controllers/login.js

@@ -0,0 +1,21 @@
+import Ember from 'ember';
+
+const { Controller, inject: { service } } = Ember;
+
+export default Controller.extend({
+  session: service(),
+  flashMessages: service(),
+
+  actions: {
+    authenticate() {
+      this.transitionToRoute('loading').then(() => {
+        let { identification, password } = this.getProperties('identification', 'password');
+        this.get('session').authenticate('authenticator:application', identification, password).catch((reason) => {
+          this.transitionToRoute('login').then(() => {
+            this.get('flashMessages').danger(reason.non_field_errors || reason);
+          });
+        });
+      });
+    },
+  },
+});