This removes:
- The now obsolete quadrature_loop_statement.
- Quadrature weights are now a globalarg and we do not create a
temporary anymore.

[Fix] Make pytest pass



See merge request !49

Feature/next sumfac

Next generation towards sum factorization
* fixes #49 by introducing an interface class between visitor and generator functions

See merge request !48

In sum factorization we will have different temporary shape and access.

and use it as the only sumfact test until it works.

* Enable backend functions which are *not* generators
* Use the sumfac switch as a default switch

The backend selecting mechanism needs all modules to be imported.
This commit restructures the package to be able to do that. Placement
of some functions felt weird, but this can still be changed.
No more placements in __init__.py anymore though, as this will
result in cyclic dependencies.

Sum factorization!

This is the new merge requests that supersedes both !42 and !45.

Also bumps submodules in various places, as loopy has had a rough week.

Also fixes #47, #20 .

See merge request !47

With some upstreamed fixes relevant to us.

Needs a small fix in loopy (MR opened).

It is a memory reinterpretation

... instead of reimplementing it all over the place

It otherwise is a pain to debug problems arising in cgen.

Merge branch 'feature/sumfactorization' of ssh://parcomp-git.iwr.uni-heidelberg.de:20022/dominic/dune-perftool into feature/sumfactorization

Conflicts:
	python/dune/perftool/sumfact/amatrix.py

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