New interfaces IDataModelListener, IDataModelObservable

[GoogleCodeExporter]

IDataModel should extend the new interface IDataModelObservable that allows to 
add and remove IDataModelListener.

The IDataModelListener should have the following methods:

beforeLoad(IVetoable veto)

afterLoadSuccess()

afterLoadError()

afterLoadCancel()

beforeSave(IVetoable veto)

afterSaveSuccess()

afterSaveError()

afterSaveCancel()

beforeUndo(IVetoable veto)

afterUndo();

beforeClear(IVetoable veto)

afterClear();

Original issue reported on code.google.com by [email protected] on 16 Mar 2013 at 1:54