refactor backups add capability

[tablatronix]

create class or proceedural methods for backups, add ability to keep more than one backup, user settable.

Add hooks also.
Add anything else necessary for a plugin to add a diffing capability.

[cnb]

👍

[tablatronix]

create functions for abstraction and security, will be sandboxed to respective folders.
backup
backuppage
restorepage
deletepage

we already have most of these, just are not using them.

[tablatronix]

Changedata does not use createBak, it uses its own copy.

createBak creates files as $file.".bak"

refactor all backup methods to use the function, unless a file is modified to be a different file perhaps we should not change the extension.

however, the undo functionality is not compatible with that. which would indicate that the pages undo does not use the undo function either.

pages uses its own copy for backing up, and restore_bak to undo via backup-edit.php
somewhat inconsistent, would be nice to normalize this stuff.