Use cli in messages

[olivroy]

fix #956

This is a rough draft. I would understand you'd rather take this on yourself, but in case it could be of any use, I thought I'd share!

Edit: CI won't cooperate. but anyway. I will try this branch of usethis installed locally and will update if something goes wrong.

Edit2 : feel free to take anything that you like from this!

List of problems

• Can't figure out how to have red bullets.

Nice to have?

ui_code that is meant to be run and other that is not meant?

Results

Impact of changes in be8a0f0

not covered by tests

• git_sitrep(): may be a problem as it uses `ui_todo with multiple lines input extensively, and is not really tested)
• pr_push()