Add prefix to write and add log message for load
Fix offsets and particle info table for parallelIO

 - improve description of domain offsets/sizes
 - add scalar position for GPUs
 - rename mpi size and rank in CommunicatorMPI
 - add 5D particles_info table to HDF5 to allow particle restarts
 - fix offsets for writing/reading fields
 - allow virtual slides at restart (re-create last GPU/position configuration)
 - change std::cout to pic log messages