Shapes cannot be deleted with Del-key in itom1dqwtplot

[M. Gronle]

The single shape deletion only works in itom2dqwtplot. It should also work in itom1dqwtplot.

[M. Gronle]

There are more issues when deleting single points from polygons:

1. The new selected index is not always correct
2. When the last point is deleted, the entire polygon is not deleted
3. The polygon becomes “open” when at least one point has been deleted

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[M. Gronle]

Fixes issue #35: Single point deletion of polygon shapes is now fixed and can also be triggered by the Del-key in the itom1dqwtplot.

→ <<cset 9253c68e53f2>>