[spgridFactory] added constructor using overlap
Use #if instead of #ifdef

HAVE_EIGEN was set to zero for me.
restructured heterogeneous projection
added MsFEM projection averaging between values
"fixed" segfault

I'm not sure whether this is really a fix or 
if I am just not seeing the segfault any more
Don't derive MsFEM projection (static members)
[cmake] tighten Eigen test
[la.container.eigen] resolve EigenBaseVector issue for good?
[common.configtree] comment unused argument
[la.container.interfaces] added operator<< for matrices
* this is a first draft and mostly meant for small dense matrices
[la.solver] check for nan or inf
[la.container.interfaces] fix operator<< friend declaration
[la.solver] let post_check_solves_system default to 1e-5
* otherwise the test in dune-gdt fails for Spe10Model1
[common.crtp] make types and methods public
* this way one can call as_imp() when matching against an interface
[functions.combined] minor change in name of difference
[functions.interfaces] update visualization
* make subsampling optional, but default to it
* make vtk output type optional and default to appendedraw
[la.container.interfaces] derive from CRTP publicly
[functions.interfaces] added operator-
[common.vector] removed obsolete specialization of clear()
[la.container.interfaces] disable warnings for dynvector