Somehow manage to fix the sizing bugs

Summary:
Remove a single `vertical-align: top`, and somewhow it now works. May
the gods of CSS have mercy on us. Also added some tests.

Test Plan:
 - See that the huxley tests don't have any changes
 - See that the new huxley screenshots look reasonable
 - Run the normal tests and see that they work

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D7494

test/huxley/Sizing.huxley/record.json

@@ -0,0 +1 @@
+{"py/object": "huxley.run.Test", "screen_size": {"py/tuple": [1024, 768]}, "steps": [{"py/object": "huxley.steps.ScreenshotTestStep", "index": 0, "offset_time": 0}]}