dojox.image.LightboxDialog has per class _groups attribute

[ramunask]

1. Create dojox.image.LightboxDialog? instance and add several images
2. Destroy first LightboxDialog? instance and create another one and add several images with the same group name as in first case.
3. Call show on second LightboxDialog? instance and you will see all images from both instances (even if first one is destroyed).

_groups attribute of LightboxDialog? class should be initialized in constructor.

[Adam Peller]

you're it.

[dante]

(In [22511]) fixes #11123. buidup a group or default