frontend performance / extensibility tweaks
- fixes #21 (closed), which was the cause of some D3 charts pages caught in an infinite loop (this problem also exists on the LLNL repository, for example https://software.llnl.gov/repo/#/LLNL/Aluminum
- Reformat HTML layout structure so that specific CSS files can always be included at the end of the
<head>
in the layout, instead of in the middle of the<body>
. This significantly improves load times. - Make the background image an actual background image to improve load times