Changed return type of BackupToFolder to BackupResultHelper.

StartBackup now returns the BackupResultHelper from each of the three save methods OR it returns an error result helper.

MainViewModel's ExecuteStartBackup now utilizes a switch.
Backup Button
Added time countdown textblock to UI,
Added countdown
Countdown timer and interval changes working correctly. In Interval setter, calling new method: BackupAuto.ChangeInterval(