Qt 5.14 adds a "--help-all" option, so include it in the autocompletion.
Qt 5.14 also warns on multiple additions of the same option, which we
accidently did (KAboutData and we ourselves called it), so don't do
that.
Also fixes device autocompletion, which I accidently broke.
Main changes:
- Allow grouping single-letter options (current single letter options
are exclusive, but that might change in the future. Qt supports
parsing such groups)
- Allowing completions like "-d<id>" and "--device=<id>"
- Make operations exclusive in completion (e.g. --ping and --ring can't
be used at the same time)
