Encapsulate python-gnupg code into its own backend class.

mayan/apps/django_gpg/runtime.py

@@ -0,0 +1,10 @@
+from django.utils.module_loading import import_string
+
+from .settings import setting_gpg_path
+
+# TODO: This will become an setting option in 2.2
+SETTING_GPG_BACKEND = 'django_gpg.classes.PythonGNUPGBackend'
+
+gpg_backend = import_string(SETTING_GPG_BACKEND)(
+    binary_path=setting_gpg_path.value
+)