Prepare database module for the Mobile app

• Move most of the code from view.php to functions
• Add required web services
• Implement the check_updates callback

Since most of the code of this module is very very old, we will be moving code from view.php to functions in mod/data/lib.php

Spec: https://docs.google.com/document/d/13NUR-DCl_B1MqzAOCfgJ6gOP6sBygeY-4kj3xs8-mDM/edit#heading=h.b67ysqmbsw6q