Modified the BackupFolder Attribute
Modified the BackupFolder Attribute

- Marked the place where a read/write test needs to be done to the backup folder, to verify permissions. This is required since NAppUpdate uses $AppFolder\Backup as the default backup folder, and some applications may not have permissions to write to it.
- Added check to see if a Backup Directory already exists, if so delete it first - otherwise we might get conflicts.
- Now you can specify a absolute dir if required, otherwise you can specify a relative dir and have it based off of the TempDir you should specify manually. This means that if TempDir is in a program writable location as it should be then BackupDir is pretty much guaranteed to be also.

Patch courtesy Jamie Lennox

synhershko/NAppUpdate,jinlook/NAppUpdate,miguel-misstipsi/NAppUpdate2,piotrwest/NAppUpdateMono,johnrossell/NAppUpdate,piotrwest/NAppUpdateMono,halotron/NAppUpdate,lexruster/NAppUpdate,yanpearson/NAppUpdate,group6tech/NAppUpdate2,vbjay/NAppUpdate