Document signatures: Rename settings

Rename the setting "SIGNATURES_STORAGE_BACKEND" to
"DOCUMENT_SIGNATURES_STORAGE_BACKEND" and the setting
"SIGNATURES_STORAGE_BACKEND_ARGUMENTS" to
"DOCUMENT_SIGNATURES_STORAGE_BACKEND_ARGUMENTS". This is
to differentiate these from the settings of the django_gpg
app.

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

HISTORY.rst

@@ -145,7 +145,12 @@
 - Removed the settings SIGNATURES_GPG_PATH. The path to the
   GPG binary is now passed via the
   SIGNATURES_GPG_BACKEND_ARGUMENTS.
-
+- Renamed the setting ``SIGNATURES_STORAGE_BACKEND`` to
+  ``DOCUMENT_SIGNATURES_STORAGE_BACKEND`` and the setting
+  ``SIGNATURES_STORAGE_BACKEND_ARGUMENTS`` to
+  ``DOCUMENT_SIGNATURES_STORAGE_BACKEND_ARGUMENTS``. This
+  change differentiates them from the setting from the 
+  django_gpg app.
 
 3.1.9 (2018-11-01)
 ==================

mayan/apps/document_signatures/settings.py

@@ -10,13 +10,13 @@ from mayan.apps.smart_settings import Namespace
 namespace = Namespace(name='signatures', label=_('Document signatures'))
 setting_storage_backend = namespace.add_setting(
     default='django.core.files.storage.FileSystemStorage',
-    global_name='SIGNATURES_STORAGE_BACKEND', help_text=_(
+    global_name='DOCUMENT_SIGNATURES_STORAGE_BACKEND', help_text=_(
         'Path to the Storage subclass to use when storing detached '
         'signatures.'
     )
 )
 setting_storage_backend_arguments = namespace.add_setting(
-    global_name='SIGNATURES_STORAGE_BACKEND_ARGUMENTS',
+    global_name='DOCUMENT_SIGNATURES_STORAGE_BACKEND_ARGUMENTS',
     default={
         'location': os.path.join(settings.MEDIA_ROOT, 'document_signatures')
     }, help_text=_(