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/document_indexing/tasks.py

@@ -5,8 +5,8 @@ import logging
 from django.apps import apps
 from django.db import OperationalError
 
+from mayan.apps.lock_manager import LockError
 from mayan.celery import app
-from lock_manager import LockError
 
 from .literals import RETRY_DELAY