Improve some modal action buttons (#24289)
Follow #24097 and #24285
And add a devtest page for modal action button testing.
http://localhost:3000/devtest/fomantic-modal
Now the `modal_actions_confirm.tmpl` could support: green / blue /
yellow positive buttons, the negative button is "secondary".
ps: this PR is only a small improvement, there are still a lot of
buttons not having proper colors. In the future these buttons could be
improved by this approach.
These buttons could also be improved according to the conclusion of
#24285 in the future.
And add GitHub-like single danger button (context:
https://github.com/go-gitea/gitea/issues/24285#issuecomment-1519100312)
---------
Co-authored-by: silverwind <me@silverwind.io>
