Added: Module Manifest; Get-NetBackupStatusCode

Added a module manifest for easier versioning, etc. Even though it wasn't on the 'To-Do' list, I added the Get-NetBackupStatusCode function which uses a basic switch block to return the status message associated to the provided status code. This has been reported by our NBU admins as being helpful at my organization for basic troubleshooting. I put it at the bottom of the .psm1 since it added so many lines.