Consolidate <script> tags in the diff viewer and reviews.

Every time the browser encounters a <script> tag, it blocks any
downloads or processing of files until that tag has finished. In our
case, it also makes things difficult for require.js, because most of our
<script> tags depend on our objects, which may not be loaded yet.

Now, we just move all the initialization into the same <script> that
sets up the page. That helps code readability and solves a lot of these
issues.

In the case of the diff viewer, I've also moved the scripts-post block
to the end of the file, to put it in page order. Along with that, I
removed the file index at the footer, since it no longer works and will
be replaced anyway.