Fix #372 -- Plugin hook for "Copy from event"

src/pretix/base/models/event.py

@@ -226,6 +226,8 @@ class Event(LoggedModel):
 
     def copy_data_from(self, other):
         from . import ItemAddOn, ItemCategory, Item, Question, Quota
+        from ..signals import event_copy_data
+
         self.plugins = other.plugins
         self.save()
 
@@ -297,6 +299,8 @@ class Event(LoggedModel):
                 s.value = 'file://' + newname
             s.save()
 
+        event_copy_data.send(sender=self, other=other)
+
 
 def generate_invite_token():
     return get_random_string(length=32, allowed_chars=string.ascii_lowercase + string.digits)