Add interface with Blender

[schlegelp]

• would need wrappers to dump neuron morphology, connectors, volumes and dotprops in Blender ( .plot_b3d() ?)
• could keep objects/collections as classes with wrappers to change basic parameters (color, bevel, size (for connectors), layers, visibility, transparency), select or unselect, and remove objects
• wrappers for clustering

[schlegelp]

Could also make a UI part of that module

[schlegelp]

Basic interface added with commit f689e1c6b2deddec01d029defc756a9f69d28038

[schlegelp]

I reopened this issue for tracking additional feature suggestions regarding the Blender integration after the initial implementation.

[schlegelp]

Reimport from Blender back to Python as core.CatmaidNeuron/List object: this would allow to load a neuron into Blender, manipulate (i.e. cut or prune) and then bring it back to Python. This would require to save treenode IDs with neuron objects -->curve.spline.points does unfortunately not allow assigning of custom properties. But we could hijack the weight property to store the treenode ID. This property is preserved when deleting points/splines but new points will get the weight of their parent!

[schlegelp]

Upon initialising b3d.handler, add new method plotb3d() to core.CatmaidNeuron and core.CatmaidNeuronList. Can be defined within the b3d module.

[schlegelp]

Generate url to 3d cursor location.