Support Modifying Built-in Domain Properties

[breezewish]

Currently we have to modify the source code in order to change the properties in system domain, which is not friendly for other custom-deployed users.

Proposal:

• Change the semantic "built-in" into "default".
• Introduce an initialization step in initial deployment (i.e. install), in which we assign default properties for the system domain in the database.
• After installation, all meta data of the system domain are retrieved from the database, just as other domains, so that they can be modified through the user interface.

@iceb0y @twd2

[Ivecia]

That's cool.

[twd2]

It's slow.

[breezewish]

We could cache the domain property for hot domains, which is easy to implement while effective.