Loading spinners for realtime images index

These spinners disappear when images are loaded.

Part of the way on #98.
Add loading spinners and text to realtime images

Fixes #98
Add skeleton sensor types page
Build of Sensor Types page
Uploaded terminus monitoring system image
Add table of contents to sensor types page
Whitespace cleanup
Skeleton out the climate station diagram pages
Station Diagram upload
Guard default content on page-wide

Just in case pages don't have html.
Clean up climate station diagram images
Include style variables in chart
Load random images into the narrow page sidebar

The number of these images is determined dynamically by the height of
the page.

Fixes #63