Another problem (sorry...)
When executing runClient, the client will start and then crash with the following report:
http://pastebin.com/cN8mzY2Y
(The same with runServer)

In the full log, there's this line
Skipping event FMLPreInitializationEvent and marking errored mod Natura since required dependency Mantle has errored
But Mantle seems to be loaded

The dev environment is otherwise working and I'm able to build the mod and use the build in a seperate Minecraft instance.

This is an issue with mantle crashing. I dont think we need it so I will remove it.