Fix OpenSeadragon to be more efficient

Tiles are 512x512 to reduce network overhead, overlap is 0 instead of 1,
and we allow up to 30 seconds for tiles to load
Add example for caching thumbnails
Simplify and expand bot rules

Blocks all bots instead of just named bots, and blocks thumbnails since
they're all dynamically generated and bots can really slow the site down
Use new tile URL

Allows for easier proxying to external image server