v0.12.1

This release fixes bugs and completes missing translation strings.

• Clarify repository menu labels for initializing vs. adding existing repos (#2509)
• Turn off Sparkle's automatic update checks when updates are disabled (#2583)
• Don't count a check that found inconsistencies as a validation (#2591)
• Fix extract dialog crash on Borg 2.0 archives and sort type errors
• Skip migration steps that add an already-existing column (#2587)
• Complete and review translations for all 12 supported locales; fix translation contexts, interpolation and plurals