Django GPG: Setting options changes

Remove the SIGNATURES_GPG_HOME settings. The GPG keys are no longer
stored in disk but in the database itself making this setting obsolete.
This changed happened several versions ago and this removal doesn't affect
any code path.

Add two new settings to the app: SIGNATURES_GPG_BACKEND and
SIGNATURES_GPG_BACKEND_ARGUMENTS. These settings allow changing the
GPG backend that the app will use.

Remove the settings SIGNATURES_GPG_PATH. The path to the GPG binary
is now passed via the SIGNATURES_GPG_BACKEND_ARGUMENTS.

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

mayan/apps/django_gpg/classes.py

@@ -10,7 +10,8 @@ from mayan.apps.common.utils import mkdtemp
 
 
 class GPGBackend(object):
-    def __init__(self, **kwargs):
+    def __init__(self, gpg_path, **kwargs):
+        self.gpg_path = gpg_path
         self.kwargs = kwargs
 
 
@@ -76,7 +77,7 @@ class PythonGNUPGBackend(GPGBackend):
         os.chmod(temporary_directory, 0x1C0)
 
         gpg = gnupg.GPG(
-            gnupghome=temporary_directory, gpgbinary=self.kwargs['binary_path']
+            gnupghome=temporary_directory, gpgbinary=self.gpg_path
         )
 
         result = function(gpg=gpg, **kwargs)