Refactor P2P and MPI handling #22

Job	Run time
Format / Links	15s
Format / pre-commit	25s
Integration / Dummy	1m 14s
PIP / Install	1m 3s
Build Cache / OpenMPI 5	34s
Domain Decomp / Unit	1m 5s
Adaptivity Serial / Unit & Integration	1m 4s
User-Side / Unit	1m 57s
Adaptivity Parallel / Unit	1m 9s
Coverage / Evaluate	1m 46s
Adaptivity Parallel / Integration	1m 18s
	11m 50s

Provide feedback