A common key listener implementation for SWT. It is applied to all widgets.
Derived forms exists for special SWT-widgets.
This class is instanciated one time in the SwtMng.
A Widget can be completed with this key listener. On all keys
the GralUserAction given in the GralWidget#getActionChange() is called
If the method returns false, the central key action given in GralMng#getRegisteredUserAction(String)
for "keyAction" is tried to get and then invoked with cmd = "key" and the key code in params.
This central keyAction may be used for application centralized keys without association to the table itself.
This method can be overridden by specialized classes of this.
This method is called firstly.
Note if a special key should be handled in the GralWidget#getActionChange()
then this special handling should be programmed in the derived class.
If this method returns true, the key is not applied to the action and not applied to the common handling.