Update links to use https:// where it is supported. There's probably a lot
more that could be fixed, but these are the core ones I found (especially
the download links in order to prevent MITM attacks). Note that there are
some fb.me links that will redirect to http:// even while accessed over
https://, but this seemed like the best way to fix those for now.
NOTE: Only non-third-party files were modified. There are references to
http:// URLs in vendored/third-party files, but seems appropriate to fix
upstream for those rather than editing the files.
Also, copy one image locally to the blog, as it was hotlinking to a site
that did not support https://.
Last, use youtube-nocookie.com instead of youtube.com for video embeds,
as the former doesn't try to set a cookie on load (privacy enhancement).
This doesn't actually remove the pages, just the main content. Sidebar
items now link offsite. The pages doesn't automatically redirect, but we
could do that if we really wanted.
Fixes#2229
