bic in kactivities

[Ivan Čukić]

Marco, thanks for reverting this.

@Laurent

The proper change for the constructor should be to make the Private class
take the shownStates by value (a sink constructor argument) and for the
ActivitiesModel constructor to std::move it when passing to the Private
constructor.

@All

- ` explicit` should not change the ABI (will have to check just in case)
- The second change that shouldn't be a problem is that
src/imports/resourcemodel.h does not need to keep ABI  - it not exported as
a normal library, it is a QML type.

This does not need the FIXME KF6 tag, the API is as it should be,

Cheers,
Ivan