'Save options' setting is global rather than per file

[Bentroen]

Issue
The 'Save options' (save version) setting seems to be global rather than per open song, which may not be intended.

Platform
Windows 10

Steps to reproduce:

1. Open two songs, one in each tab
2. Open 'Save options' and set song 1 to 'v5'.
3. Change the currently selected tab to to song 2.
4. Open 'Save options' again.

• -> The song will be in v5 too.

Expected behavior
Each song should store its own save setting, such that changing this setting for one song doesn't interfere with other open songs.

Screenshots

Additional context
This has been tested in 3.12 Beta 1, but the issue is likely to persist on Beta 2.