lib: improve representation of “default-shells”
lib: complete `Host.of_uri` with default-shell
lib: fix `EDSL.make` and add `EDSL.run`
test: convert `deploy_website` to the EDSL
test: use `EDSL.run` everywhere
lib: remove `workflow` parts of the EDSL

The function `run` is clear enough.
build: update `get-dependencies` sub-command