#53 property change in viewer config

[Antonio S. R. Gomes]

The property sheet for viewer configurations works now
only one-way (they can set the property in the target
viewer), but if cannot listen to property changes the
target viewer.

For instance, suppose you just opened two viewer config
property sheets (that is, two internal frames). If you
change a property in one of them the other will not see
any change at all. You have to reopen the property
sheet to reflect the changes. This may happend if the
viewer has its all config dialog, for instance.

This can be solved using property change listeners
(Java Bean spec) for each bean propery being edited.