Website improvements TODO

[ceball]

• put full-sized logo with wordmark on homepage
• add param(bokeh) style (currently just default nbsite)
• make sure logo is transparent, scalable, etc. if appropriate for each version
• add gallery
• name user guide pages with numbers (but see Consistent notebook titles (and handle options/variations?) holoviz-dev/nbsite#18)
• deploy website for commits to master to an alternative address [testing: https://ioam-docs.github.io/parambokeh-master/)
• deploy website for PRs to an alternative address
• indicate/allow selection of version on website (depends on auto versioning)