Rebuild the fallback list in late 2019 or early 2020

Late in 2019, or early in 2020, we should rebuild the fallback list again.

We usually do this when 25% or more go down. (When 25% of fallbacks are down, a warning is logged daily in #tor-bots on IRC, and via email to the fallback maintainers.)

Here are the instructions for running a rebuild: https://trac.torproject.org/projects/tor/wiki/doc/UpdatingFallbackDirectoryMirrors

See the child tickets for each step.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information