Changed plugin URL config to create better error messages,

fixed an import error

src/pretix/plugins/banktransfer/views.py

@@ -9,12 +9,10 @@ from decimal import Decimal
 from django import forms
 from django.contrib import messages
 from django.shortcuts import redirect, render
-from django.utils.decorators import method_decorator
+from django.utils.functional import cached_property
 from django.utils.timezone import now
 from django.utils.translation import ugettext_lazy as _
-from django.views.decorators.debug import sensitive_post_parameters
 from django.views.generic import TemplateView
-from pip.utils import cached_property
 
 from pretix.base.models import Order, Quota
 from pretix.base.services.orders import mark_order_paid

src/pretix/urls.py

@@ -1,4 +1,4 @@
-import importlib
+import importlib.util
 
 from django.apps import apps
 from django.conf import settings
@@ -22,13 +22,11 @@ if settings.DEBUG:
 pluginpatterns = []
 for app in apps.get_app_configs():
     if hasattr(app, 'PretixPluginMeta'):
-        try:
+        if importlib.util.find_spec(app.name + '.urls'):
             urlmod = importlib.import_module(app.name + '.urls')
             pluginpatterns.append(
                 url(r'', include(urlmod, namespace=app.label))
             )
-        except ImportError:
-            pass
 urlpatterns.append(
     url(r'', include(pluginpatterns, namespace='plugins'))
 )