Conflicts:
	python/dune/perftool/pdelab/quadrature.py

Add vectorization support to dune-perftool

See merge request !58

Do not use continue stuff. Instead precompute the quantities.

Feature/memory fences

TODOS
* [x] General infrastructure to issue barriers
* [x] Actually implement the barrier in `DuneTarget`
* [ ] Identify the spots in sum factorization where barriers are necessary

This fixes #46 

See merge request !55

Feature/sumfact poisson

See merge request !59