Added datamean field to GPU, removed tmp3 again (was only used during testing)
Renamed the xGPU routines to default convection of _g
Added function to calculate mean profile on GPU
Merge remote-tracking branch 'chiel/cuda' into cuda

Conflicts:
	include/grid.h
	src/fields.cu
	src/grid.cu
Cleanup merge and renaming of functions, reduced output moser180