Added documentation for Material, Export, Comment, Switch and Remote nodes.
Fixed missing "tool" attribute in editable_label script.
Reordered misc. nodes in base library.
Now linking new controls to a linked_control will check compatibility (same control type and parameters).
Linked control labels are now editable.
Modified the Switch node layout so it is easier to understand.
Updated the bricks example to use the switch and remote nodes.
Added a class for gradient (that handles serialization and shader generation), and updated the GradientEditor.
Added a "Types" class that handles values serialization.
Updated linked_control and config_control to link to GradientEditors.
Started adding the "remote" node, that can control important parameters of the graph and save/restore configurations of groups of parameters. This should help creating easily configurable materials.
Added new "mosaic" example
Exporting a material will now create a SpatialMaterial. The Material graph node
now generates different textures when used as a Godot addon (metallic, roughness
and ambient occlusion are merged into a single texture).
Rendering code (that was in graph_edit and node_base scenes) is now in a single "renderer scene" attached to the main window.
