Add huxley screenshot tests

Summary:
Add in a testing page, which just renders the location hash in the body. Use
this to make some screenshot tests in huxley. Note, these screenshots were made
in Firefox on a Linux computer, so running the tests somewhere else might
produce something else.

Test Plan:
- Serve KaTeX (`make serve`)
- Run a Selenium Server (I used selenium 2.40.0)
- Run `huxley` from the test/huxley/ directory
- Ensure that all of the tests pass

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D7258

test/huxley/Huxleyfile

@@ -0,0 +1,32 @@
+[BasicTest]
+url=http://localhost:7936/test/huxley/test.html#a
+
+[FractionTest]
+url=http://localhost:7936/test/huxley/test.html#\dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}
+
+[NestedFractions]
+url=http://localhost:7936/test/huxley/test.html#\dfrac{\frac{a}{b}}{\frac{c}{d}}\dfrac{\dfrac{a}{b}}{\dfrac{c}{d}}\frac{\frac{a}{b}}{\frac{c}{d}}
+
+[Exponents]
+url=http://localhost:7936/test/huxley/test.html#a^{a^a_a}_{a^a_a}
+
+[Colors]
+url=http://localhost:7936/test/huxley/test.html#\blue{a}\green{b}\red{c}
+
+[GreekLetters]
+url=http://localhost:7936/test/huxley/test.html#\alpha\beta\gamma\omega
+
+[Baseline]
+url=http://localhost:7936/test/huxley/test.html#a+b-c\cdot d/e
+
+[Spacing]
+url=http://localhost:7936/test/huxley/test.html#[-1][1-1]1=1(=1)\lvert a\rvert
+
+[Functions]
+url=http://localhost:7936/test/huxley/test.html#\sin\cos\tan\ln\log
+
+[Lap]
+url=http://localhost:7936/test/huxley/test.html#ab\llap{f}cd\rlap{g}h
+
+[KaTeX]
+url=http://localhost:7936/test/huxley/test.html#\KaTeX