Fixing a save bug that occurs when changing a request/folder name

[APIWT]

If you were to save a workbook after changing a request or folder name, it would take the following actions:

• Use the in-memory filesystem to create a workbook.json file with the details of the workbook.
• Loop through the in-memory workbook's folders and requests, then create a file on the host filesystem.

However, as a result, it ends up leaving the old (pre-renamed) request/folders on the filesystem, meaning the next time you load the workbook you end up with a duplicate.

This patch changes this behavior by instead taking these actions:

• Create a backup of the host filesystem's workbook files (workbook.json and all the folder/request JSONs) inside the .sgbackup
• Delete the host filesystem's workbook files
• Use the in-memory filesystem to create a workbook.json file with the details of the workbook.
• Loop through the in-memory workbook's folders and requests, then create a file on the host filesystem.

This seems to work, but in the future it might make sense to change this approach.

The nice thing about this approach is that it should be possible to load directly from the backup if necessary.

[APIWT]

This should fix #12