This commit allows users to put alternative wordlists in a `wordlists` subdirectory below their KeePassXC directory (e.g., under Linux, `~/.config/keepassxc/wordlists`). These wordlists will then appear in the dropdown menu in the *Password Generator* widget.
In order to differentiate between lists shipped with KeePassXC and user-provided lists, the former appears with a (SYSTEM) prefix.
The tray icon appearance setting is null by default, since we do not
want to include OSUtils into Config. As a result, we must take special
care to preselect the correct combo box entry on the settings page.
