Fix running axis_label tests via JsTestDriver - jQuery's $ isn't defined.

When running the tests via JsTestDriver, I was getting errors relating to $ not being defined.

```
$ java -jar ./auto_tests/lib/JsTestDriver-1.3.3c.jar --tests all
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..F...................................................................
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Total 257 tests (Passed: 252; Fails: 1; Errors: 4) (3053.00 ms)
  Chrome 29.0.1547.65 Mac OS: Run 257 tests (Passed: 252; Fails: 1; Errors 4) (3053.00 ms)
    axis-labels.testAxisLabelFontSize error (5.00 ms): TypeError: Property '$' of object [object Object] is not a function
      TypeError: Property '$' of object [object Object] is not a function
          at AxisLabelsTestCase.testAxisLabelFontSize (http://localhost:9876/test/auto_tests/tests/axis_labels.js:580:18)

    axis-labels.testAxisLabelFontSizeNull error (7.00 ms): TypeError: Property '$' of object [object Object] is not a function
      TypeError: Property '$' of object [object Object] is not a function
          at AxisLabelsTestCase.testAxisLabelFontSizeNull (http://localhost:9876/test/auto_tests/tests/axis_labels.js:634:18)

    axis-labels.testAxisLabelColor error (7.00 ms): TypeError: Property '$' of object [object Object] is not a function
      TypeError: Property '$' of object [object Object] is not a function
          at AxisLabelsTestCase.testAxisLabelColor (http://localhost:9876/test/auto_tests/tests/axis_labels.js:649:15)

    axis-labels.testAxisLabelColorNull error (7.00 ms): TypeError: Property '$' of object [object Object] is not a function
      TypeError: Property '$' of object [object Object] is not a function
          at AxisLabelsTestCase.testAxisLabelColorNull (http://localhost:9876/test/auto_tests/tests/axis_labels.js:703:15)

    custom-bars.testCustomBarsWithNegativeValuesInLogScale failed (16.00 ms): AssertError: expected 2 but was 3
      Error: expected 2 but was 3
          at CustomBarsTestCase.testCustomBarsWithNegativeValuesInLogScale (http://localhost:9876/test/auto_tests/tests/custom_bars.js:182:3)

Tests failed: Tests failed. See log for details.
```

(The custom-bars error seems to be a bit flaky - it only seems to pass the first time it's run)

I couldn't figure out where jQuery was meant to be pulled in, so I rewrote the tests to use window.getComputedStyle. This should work for all but IE8 and below (http://www.quirksmode.org/dom/w3c_css.html). I'm not sure if IE8 is supported? If it is I'll look for an alternative approach.