Moved 3D RBC stuff to its own project

[brownbaerchen]

I migrated everything used for the 3D RBC project so far to its own project directory. This project is now tested on CPUs on Github.
I am relying here on some files from the GPU project. We can either have a self contained project with duplicate code or do this. I opted for the latter. Let me know if you prefer the former.

[pancetta]

How much do you rely on the GPU project? Does it make sense to move the GPU part to the core routines?

[brownbaerchen]

How much do you rely on the GPU project? Does it make sense to move the GPU part to the core routines?

What I am using from there is some infrastructure for running problems i.e. I use commands like mpirun -np 256 python run_experiment --config=RBC... --procs=1/4/64 .... Parts of the GPU project then set up the space time parallelization, add hooks for some logging and output and so on. I think this is specific to my way of executing stuff, so I wouldn't put it in some core place.