Switch to full app paths

Instead of inserting the path of the apps into the Python app,
the apps are now referenced by their full import path.

This solves name clashes with external or native Python libraries.
Example: Mayan statistics app vs. Python new statistics library.

Every app reference is now prepended with 'mayan.apps'.

Existing config.yml files need to be updated manually.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/mailer/views.py

@@ -6,13 +6,13 @@ from django.template import RequestContext
 from django.urls import reverse, reverse_lazy
 from django.utils.translation import ungettext, ugettext_lazy as _
 
-from acls.models import AccessControlList
-from common.generics import (
+from mayan.apps.acls.models import AccessControlList
+from mayan.apps.common.generics import (
     FormView, MultipleObjectFormActionView, SingleObjectDeleteView,
     SingleObjectDynamicFormCreateView, SingleObjectDynamicFormEditView,
     SingleObjectListView
 )
-from documents.models import Document
+from mayan.apps.documents.models import Document
 
 from .classes import MailerBackend
 from .forms import (