[Bf-codereview] Node Copy/Paste feature (issue 6249060)

[lukas.toenne at googlemail.com]

Reviewers: bf-codereview_blender.org,

Description:
Clipboard feature for nodes. With the Copy operator a copy of all
selected nodes and links between them is stored in an offscreen list
(not in the library). The Paste operator then in turn copies these into
the active node tree in the editor.

Limitation is that animated node values will lose all animation data.
Fixing this would require copying a subset of the ID block's (node tree)
fcurves to the clipboard and then insert a copy (with redirected paths)
into the target node tree.


Please review this at http://codereview.appspot.com/6249060/

Affected files:
   source/blender/blenkernel/BKE_node.h
   source/blender/blenkernel/intern/node.c
   source/blender/editors/space_node/node_edit.c
   source/blender/editors/space_node/node_intern.h
   source/blender/editors/space_node/node_ops.c