Fresh Installs Default to Dark Theme Even if System is Light Theme

[dsanders11]

The default setting for a fresh install is for "Sync theme with system setting" to be checked, but with no theme previously set Fiddle will default to dark theme. So if a system is light theme and Fiddle is freshly installed, it will be out of sync with the system theme. This is most noticeable on Windows, where the titlebar will be matching the system light theme but the rest of the window will be using dark theme.