add event manager

auto backup removed from setting. You can now schedule backups with
the event manager

Fixes #762

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

sftpgo.json

@@ -231,12 +231,7 @@
     "create_default_admin": false,
     "naming_rules": 1,
     "is_shared": 0,
-    "backups_path": "backups",
-    "auto_backup": {
-      "enabled": true,
-      "hour": "0",
-      "day_of_week": "*"
-    }
+    "backups_path": "backups"
   },
   "httpd": {
     "bindings": [