4.15.0

- Record last commands only once (Bug #15767)
- Sort by frecency (Bug #9265)
- Switch to README.md and foreign automake mode
- Move from exo-csource to xdt-csource (Bug #16717)
- Make Preferences button always visible (Bug #16489)
- Fix gtk version checking
- Hidden option to disable entry completion (Bug #15827)
- Use casefolded string when searching for apps not commands (Bug #15893)
- Translation Updates:
  Albanian, Amharic, Arabic, Basque, Belarusian, Chinese (China), Chinese
  (Hong Kong), Chinese (Taiwan), Croatian, Danish, English (Australia),
  English (United Kingdom), Estonian, French, Galician, Greek, Hebrew,
  Hungarian, Icelandic, Indonesian, Interlingue, Italian, Korean,
  Norwegian Nynorsk, Occitan (post 1500), Romanian, Russian, Slovak,
  Slovenian, Spanish, Swedish, Telugu, Uighur, Vietnamese