WIP Details pane + contributor profiles

Adds a 3-pane layout option for showing details, as well as a dashboard
sub-route for showing contributor details in the new details pane.

app/components/user-avatar/component.js

@@ -1,11 +1,30 @@
 import Component from '@ember/component';
 import { alias } from '@ember/object/computed';
+import { computed } from '@ember/object';
+
+const SIZES = {
+  'small':  '128', // pixels
+  'medium': '256',
+  'large':  '512'
+}
 
 export default Component.extend({
   contributor: null,
   tagName: 'img',
   classNames: ['avatar'],
+  classNameBindings: ['size'],
   attributeBindings: ['src', 'title'],
-  src: alias('contributor.avatarURL'),
-  title: alias('contributor.name')
+  size: 'small',
+
+  src: alias('avatarURL'),
+  title: alias('contributor.name'),
+
+  avatarURL: computed('contributor.github_uid', 'size', function() {
+    const github_uid = this.contributor.github_uid;
+
+    if (github_uid) {
+      return `https://avatars2.githubusercontent.com/u/${github_uid}?v=3&s=${SIZES[this.size]}`;
+    }
+  })
+
 });