Store configuration settings in database

[Gavin]

Create a new AppConfig class.
The system can record events and configuration settings in this class.

e.g:

Class AppConfig {
    String name
    String value
}

This will be used for recording:

• Base data created, then can be tested to disable double creation.
• Demo data created, then can be tested to disable double creation.
• Date formats.
• and other configuration settings.

[Gavin]

Implemented in r234 and r237.