Temporary Save Files should be prepended with ~

[KazWolfe]

Microsoft convention appears to be to prepend temporary files with ~ as part of a write-save-delete operation, which we do as part of our user datfile process.

Adding the ~ to temporary files will prevent them from being auto-synced to OneDrive (possibly fixing a few issues for certain edge cases), hide them from Explorer views, and otherwise act to "tidy up" the system.