4.15.1

- Fix potential crash in suspend and shutdown (Fixes #65)
- Avoid potential format-string vulns (Issue #65)
- settings: Tweak 'Current Session' tab
- settings: Make 'App Autostart' columns sortable
- settings: Fix 'Current session' column width (!10)
- Add lock icon, 24px and 32px icons
- Add more guards around GErrors
- Update copyright year
- Fix ifdef
- Add README.md
- Translation Updates:
  Armenian (Armenia), Basque, Belarusian (Tarask), Chinese (China),
  Czech, Danish, Eastern Armenian, Estonian, French, Hebrew, Hungarian,
  Indonesian, Norwegian Bokmål, Portuguese (Brazil), Russian, Slovak,
  Slovenian, Swedish, Turkish, Uyghur