MORSE_Distributed_size, MORSE_Distributed_rank so that applications do not
hardcode the use of MPI.

Introduce RUNTIME_distributed_rank, RUNTIME_distributed_size,
RUNTIME_distributed_barrier, so that MORSE does not hardcode the use of MPI
either.

This allows to use simgrid-mpi.

add MORSE_Pause/Resume function to avoid CPU consumption when no tasks have to be executed - call starpu_pause/resume, do nothing for quark (no need)

change the way we include our own header files --> relative to the root - when plasma is in the same env, chameleon can take some headers not belonging to it (ex: #include descriptor.h, this file states in plasma install dir also) which make compilation errors

change copyright - correct whitespace - place cmake module depending on chameleon in cmake_modules and no more in cmake_modules/morse