SQLite fixes and addition to config.json schema.

sample-config-advanced.json

@@ -3,6 +3,7 @@
   "__comment__": "This is a sample configuration file, all values and sections that start with underscore (_) are ignored. Edit a section and remove the _ in front of the name. Refer to the user's guide for details.",
   "settings": {
     "_cert": "myserver.mydomain.com",
+    "_SQLite3": true,
     "_acebase": { "_sponsor": true },
     "_mongoDb": "mongodb://127.0.0.1:27017",
     "_mongoDbName": "meshcentral",