DB-API: make autobackup configurable

Via command line:

  gramps --config=database:autobackup:1    ## True
  gramps --config=database:autobackup:0    ## True

Or by editing gramps.ini.

gramps/gen/config.py

@@ -159,6 +159,7 @@ register('behavior.addons-url', "https://raw.githubusercontent.com/gramps-projec
 
 register('database.backend', 'bsddb')
 register('database.compress-backup', True)
+register('database.autobackup', True) ## make backup when exiting, if there are changes
 register('database.path', os.path.join(HOME_DIR, 'grampsdb'))
 
 register('export.proxy-order',

gramps/gen/db/generic.py

@@ -1795,7 +1795,8 @@ class DbGeneric(DbWriteBase, DbReadBase, UpdateCallback, Callback):
         """
         if self._directory:
             if update:
-                self.autobackup(user)
+                if config.get('database.autobackup'):
+                    self.autobackup(user)
                 # This is just a dummy file to indicate last modified time of the
                 # database for gramps.cli.clidbman:
                 filename = os.path.join(self._directory, "meta_data.db")