Martin Dobias ea1716261a Make sure that also groups with "required" layers cannot be removed
Fixes an unreported bug where it was possible to select a layer tree group
and remove even when it contained required layers.

When removing layers/groups, the following checks will now also recursively
test layers and not just directly selected layers:
- test for layers with unsaved changes
- test for layers with active tasks running in background
2018-09-26 09:55:37 +02:00
..