Export Rules as YAML MacOS filename issue

[gerrycampion]

Problem

Refer to the issue noted here: #213 (comment)

"I believe this could be an issue specific to Mac OS. When files are created, they use a filename format like: RuleID.UUID.yml
If a rule is missing a RuleID (There are currently 4 such rules), the filename will begin with a dot. MacOS treats these as hidden files."

Solution

The export functionality should use a placeholder for missing RuleIDs so that filenames do not start with periods.