Store plClient password using platform-specific credential storage.

Add an abstracted password-storage system, and utilize it in plClient to replace the drive-based obfuscation.
Can we figure out a plan of action for this? I understand why the product UUIDs are the same for repair functionality, but it's a really broken system when you can't rely on the one thing that should be guaranteed unique >.<

Maybe we add a reverse domain style "friendly name" (org.guildofwriters.gehn, com.cyan.urulive, etc.) for this sort of thing?