A dialog for File->Merge

[micheus]

Here is the latest dialog appearance:

(1) is now different for Objects/Light, Materials and Images.
- It was added a option to import only the materials used by the objects being imported;
- the images list shows if an image is external (otherwise it is internal).
(2) Each checkbox will be enabled only if its respective elements exists;
(3) As already pointed in the post #43, the three radio buttons will be enabled if there is any selection in the scene being imported; otherwise by checking "Make all new selection" (I still didn't change this title) you will be able to select between "Add to Current" and "Replace the current" (only).

I hope you guys could test it, since I think this first version is finished.

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Lets put the link for download here again: Merge Dialog - please test it.