Recover warning when new issue type / priority scheme does not cover all existing issues in a project

In versions 2.X of PC an import produced a warning if the new issue type or priority scheme for a project did not include issue types / priorities for all issues in the project. These issues were not lost or corrupted, but from a logical point of view this is an inconsistency in the new configuration, so it was good to warn the user.

This warning has been lost with PC 3.0.0

A similar situation may arise when an issue type/priority scheme already in use by some projects is modified so that some issue types / priorities are removed from it.

This fix recovers the warning in both cases for versions 3.X of Project Configurator.