Nested projects: cancel button actually imports data
### Description / Beschreibung

In nested projects if someone opens the import from parent project and then decides not to import anything by clicking <kbd>Cancel</kbd> the data will be imported anyway.

### Expected behaviour / Erwartetes Verhalten

Expected behaviour is to get back to the project details view without any changes to the answers, i.e. not importing anything from the parent project.

### Steps to reproduce / Schritte zum Reproduzieren

1. Create a project and add some answers
2. Create a child project
3. In the child project go the import from parent project view
4. Click <kbd>Cancel</kbd> button
5. Answers are imported to the child project.


diff --git a/rdmo/projects/mixins.py b/rdmo/projects/mixins.py
index 1cec2750..c506de83 100644
--- a/rdmo/projects/mixins.py
+++ b/rdmo/projects/mixins.py
@@ -204,6 +204,12 @@ class ProjectImportMixin(object):
     def import_project(self):
         current_project = self.object
 
+        if 'cancel' in self.request.POST:
+            if current_project:
+                return HttpResponseRedirect(current_project.get_absolute_url())
+            else:
+                return HttpResponseRedirect(self.success_url)
+
         # get the original project
         project = get_object_or_404(Project.objects.all(), id=self.request.POST.get('source'))
 
['rdmo/projects/mixins.py']