Add custom nodes to example trees

[tkeskita]

Some of the custom nodes are not currently applied in any example tree. If they were, it would give users an example how to use custom nodes, as well as developers an easy way to test for regression bugs. I'm going to increase the coverage. Here is a list of current status of custom nodes and example trees (UPDATED):

customfilter.py:

• Custom Filter - cubeflow_filter_test
• Multi Block Leaf - cubeflow_*
• Time Selector - cubeflow_*
• VTKImageData Object Source - cubeflow_openvdb_export
• Global Time Keeper - none, requires setting of keyframes, see test/test_global_time_keeper.py and test/blend_files/test_global_time_keeper.blend

info.py:

• Info - cubeflow_base_boundary

colormap.py:

• Color Mapper - many, e.g. cone
• Color Ramp - many, e.g. cone

converters.py:

• VTK To Blender Mesh - many, e.g. cone
• VTK To Blender Particles - cubeflow_particle_instancing
• VTK To OpenVDB Exporter - cubeflow_openvdb_export
• VTK To Blender Image - cubeflow_cut_plane_to_image

custom_nodes/VTKFilters.py:

• VTKContourFilter - cubeflow_contours, head
• VTKMarchingCubes - cubeflow_filter_test
• VTKAppendFilter - cubeflow_filter_test
• VTKThreshold - cubeflow_filter_test
• VTKBoxClipDataSet - cubeflow_filter_test
• VTKTransformFilter - cubeflow_filter_test

custom_nodes/VTKOthers.py:

• VTKPlane - many, e.g. clip
• VTKSphere - clip

[tkeskita]

Now all nodes should be used in some example node tree.