Q_ASSERT on editing "comment" annotation

The issue is reproduced in the debug mode only.

Scenario:

1. Open Sequence View for "murine.gb".
2. Select "comment" annotation.
3. Attempt to open "Edit Annotation" dialog (e. g. select "Edit > Annotation" in the context menu).
   Current result: Q_ASSERT is triggered in "CreateAnnotationFullWidget::setAnnotationType(U2FeatureType type)".

It is not currently clear enough how the issue should be fixed. Ideally, info currently stored in the "comment" annotation should be visualized in some other way. An easier way is to prevent "comment" annotation group and "comment" annotation from editing (but note the qualifier), however, this modification should be covered by tests.