Show contributor/contribution details on mobile

Refs #163

On small screens, when selecting a contribution or contributor, the
lists are hidden and only the details are shown. The transitions are
animated using liquid-fire.

app/transitions.js

@@ -0,0 +1,25 @@
+export default function () {
+  this.transition(
+    this.fromRoute('dashboard.index'),
+    this.toRoute('dashboard.contributions'),
+    this.media('(max-width: 600px)'),
+    this.use('toLeft'),
+    this.reverse('toRight'),
+  );
+
+  this.transition(
+    this.fromRoute('dashboard.index'),
+    this.toRoute('dashboard.contributors'),
+    this.media('(max-width: 600px)'),
+    this.use('toLeft'),
+    this.reverse('toRight')
+  );
+
+  this.transition(
+    this.fromRoute('dashboard.contributions'),
+    this.toRoute('dashboard.contributors'),
+    this.media('(max-width: 600px)'),
+    this.use('toLeft'),
+    this.reverse('toRight')
+  );
+}