Refactor Avatar and AvatarOverlay to have 'account' as prop instead of src and staticSrc (#4526)

* Refactored Avatar and AvatarOverlay (DRY) to have 'account' as prop.
Also removed animate attribute from compose navigation bar, which should
have never been there. Added test for avatar overlay.

* fix broken tests

* god dammit another bug in tests! travis please let this pass

* formatting in avatar overlay

spec/javascript/components/avatar_overlay.test.js

@@ -0,0 +1,34 @@
+import { expect } from 'chai';
+import { render } from 'enzyme';
+import { fromJS }  from 'immutable';
+import React from 'react';
+import AvatarOverlay from '../../../app/javascript/mastodon/components/avatar_overlay';
+
+describe('<Avatar />', () => {
+  const account = fromJS({
+    username: 'alice',
+    acct: 'alice',
+    display_name: 'Alice',
+    avatar: '/animated/alice.gif',
+    avatar_static: '/static/alice.jpg',
+  });
+  const friend = fromJS({
+    username: 'eve',
+    acct: 'eve@blackhat.lair',
+    display_name: 'Evelyn',
+    avatar: '/animated/eve.gif',
+    avatar_static: '/static/eve.jpg',
+  });
+
+  const overlay = render(<AvatarOverlay account={account} friend={friend} />);
+
+  it('renders account static src as base of overlay avatar', () => {
+    expect(overlay.find('.account__avatar-overlay-base'))
+      .to.have.style('background-image', `url(${account.get('avatar_static')})`);
+  });
+
+  it('renders friend static src as overlay of overlay avatar', () => {
+    expect(overlay.find('.account__avatar-overlay-overlay'))
+      .to.have.style('background-image', `url(${friend.get('avatar_static')})`);
+  });
+});