File load & save error checking

* Scenemanager ( Load & save oar)
* AppearanceArchiver (load & save avatar archive)
* InventoryArchiver (load , save & save withoutassets iar file)
    - added some sanity checks for missing, invalid and existing
filenames.

* Rename WhiteCore/Modules/Region/AuroraArchiver.cs
.../WhiteCoreArchiver.cs
	(old format .abackup processing)