Plugins add datatype
MR after !152 (merged)
Almost solves #75 (closed) (need to change FTI plugin)
First step for #65 (closed) (now plugins can add datatypes)
This MR allows to easily add a new feature: supporting MPI_Types from mpi_plugin (#67 (closed))
- Removed MPI_Comm datatype from PDI core
- Added definition of MPI_Comm datatype to mpi plugin
- Added datatype map to global_context and inserted basic datatypes