[la.container.eigen] small updates * added almost_equal * added another ctor to dense matrix * added solver support (this might not be necessary)
[la.container.eigen] small updates
* added almost_equal
* added another ctor to dense matrix
* added solver support (this might not be necessary)

renemilk/DUNE-Stuff,renemilk/DUNE-Stuff,renemilk/DUNE-Stuff