Update user interface for module SystemGroup.

* DB: add field "type" to table _group, for marking group as system group.
DB: add field "type" for table "_group".

* _group.type:
	- 0 for system group.
	- <others>: user group.
* SystemGroup.data: move to directory SystemGroup/Group/.
Update framework.

* Jx.StorePaging: add property "fieldId", to mark specific field as PK.
* Jx.GridPaging:
  - split initComponent into several functions.
  - compDetails: new property, allow grid to behave like master-detail.
	Automatically refresh each component in gridDetails when row in
	master grid is selected.
SystemGroup: add grid detail "Users of Group".