Removed any default margin from body.
Merge pull request #16855 from slavingia/patch-1

Removed any default margin from mail preview body.
[ci skip] application.rb -> development.rb in web-console docs
Merge pull request #16858 from y-yagi/fix_web_console_docs

[ci skip] application.rb -> development.rb in web-console docs
Tell the user which file is missing when config/database.yml was not found

Since cc03675d30b58e28f585720dad14e947a57ff5b the error message became like
"Could not load database configuration. No such file -"
which doesn't really tell what's actually missing.
Rename from preview_path to preview_paths
Add support for multiple preview_path