Create backups of all patterns in case a theme update wipes them out

[johnstonphilip]

Just in case we have a user who uses this in production without understanding the dangers, we can create backups of the generated pattern files for them, which they can use to recover any pattern files they wiped out out by updating their theme.

How to test

1. Update/Create a pattern.
2. Notice a duplicate copy was created at /wp-content/pattern-backups/the-theme-name/
3. Delete a pattern.
4. Notice it also gets deleted from the backups.
5. Rename a pattern. Notice the backed-up version also gets renamed.

Suggested changelog entry

• Added pattern backups.

[kienstra]

Hi @johnstonphilip,
Good response to feedback, but having 2 sources of truth isn't great.

Update: Not really 2 sources of truth, as 1 is only a backup.

If a theme update wipes out the patterns, maybe they're not the ideal user.

They're probably not using GIT, which might defeat the purpose of PM.

[johnstonphilip]

Another idea: search for a .git directory in the theme root. If none exists, put a big (dismissable?) warning?

[kienstra]

Interesting, I like that more

[johnstonphilip]

Another possible replacement for this in #104