Make output option in gui mode save to the specified file path

Here's how it's supposed to work now:

- The specified file path always overrides other save file paths, unless
Save As is used in GUI mode.
- Only auto save in GUI mode if the auto save option is actually used
(GUI option)
- File paths are interpreted as local files unless a url scheme is
specified.
- Relative paths work.


(cherry picked from commit 553eb2cf)