fix test scroll

[rvilarl]

Hi Ron, please look into that, I had to undo some of your chenges in flow.html.

This PR avoids that the tests scroll behind the header.

[ronyeh]

There is still a small bug where the footer links are hidden behind the header, and one of the tests seems to be rendered off to the left. Can you investigate? We can perhaps merge the footer links into the header... since it is less likely someone will scroll all the way to the bottom of the huge page of tests.

Additionally, I had added a short sentence saying "Please wait a moment while the tests run....", which your PR removed. I think it would be useful to have that in case the tests take a long time to run. On my machine, the webpage looks broken until the tests all finish:

    <h3>
        Please wait a moment while the tests run....<br /><br />
        See the: <a id="vex-src" target="_blank"></a>. Don't forget to run the
        <a href="https://github.com/0xfe/vexflow/wiki/Visual-Regression-Tests">Visual Regression Tests</a>!
    </h3>