use directory support in gbs-downloader for a directory techdemo

obelisk/dep/gbs-downloader/git.json

obelisk/dep/tahoe-capabilities/default.nix

obelisk/dep/tahoe-capabilities/git.json

obelisk/dep/tahoe-capabilities/thunk.nix

obelisk/dep/tahoe-directory/default.nix

obelisk/dep/tahoe-directory/git.json

obelisk/dep/tahoe-directory/thunk.nix

obelisk/dep/tahoe-ssk/git.json

obelisk/frontend/frontend.cabal

obelisk/frontend/src/Pages/TechDemo.hs

obelisk/haskell-overrides.nix