Simulations: Add simulation node tree type

This implements a new builtin node tree type called `SimulationNodeTree`.
It is not yet embedded in the `Simulation` data block.

The node tree will initially be used for the new particle nodes system.

When the cmake option `WITH_NEW_SIMULATION_TYPE` is enabled, a new
`Simulation Editor` is shown in the editors menu (which is just a node editor).

This patch does not add entries to the Add Node menu, so it is empty.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D7287

source/blender/nodes/NOD_common.h

@@ -26,6 +26,10 @@
 
 #include "BKE_node.h"
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 void register_node_type_frame(void);
 void register_node_type_reroute(void);
 
@@ -42,4 +46,8 @@ struct bNodeSocket *node_group_output_find_socket(struct bNode *node, const char
 void node_group_input_update(struct bNodeTree *ntree, struct bNode *node);
 void node_group_output_update(struct bNodeTree *ntree, struct bNode *node);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* __NOD_COMMON_H__ */