Update to 2.9.0
    
    - Translation updates from Weblate for de, ja, pl, tr, uk, zh_CN
    - Update ibus-typing-booster.pot (Some new translatable strings, tooltips for 2 new buttons)
    - Improve matching of keybindings, consider IBus.ModifierType.MODIFIER_MASK
      (Resolves: https://github.com/mike-fabian/ibus-typing-booster/issues/94)
    - Show the list of dictionaries in the setup tool only if it is more than just ['None']
    - If a real dictionary is added in the setup tool, remove dummy dictionary 'None'.
    - Add black flag for the special dummy dictionary 'None'
    - Add doctests to check that the special dictionary 'None' is handled correctly
    - When the list of imes or dictionaries is emptied by the user, set it to 'NoIME' or 'None'
      (Resolves: https://github.com/mike-fabian/ibus-typing-booster/issues/98)
    - Add "Set to default" buttons for the list of input methods and dictionaries
    - Remove the special candidate which is shown when a dictionary is missing