Feat: Show sheet filenames

[sevonj]

Closes #174

This adds optional filename titles to the sheet list. The setting is off by default.

The issue asked for replacing the preview with filename, but found it more useful to show both.

Screenshots

On:

Off (exact same as before):

Settings toggle:

I couldn't build a flatpak to test if these changes break it. They really shouldn't, but I'll just point mention it.