This change fixes two major issues:
1. If you don't use SIGQUIT to stop Plex it will corrupt its own
database :(
2. Newer versions of Plex keep metadata in the
`com.plexapp.plugins.library.db` database. This is the file that
we copy into `/var/lib/plex/.skeleton`. If we copy the empty
database on top of this one the user will lose their entire
library metadata. This change skips the copy if the file
already exists.
5a50b26662