Fix compilation issue with std::isinf

Finish memory_pool implementation in container.h

Use of matrices allocated in memory pool for intermediate results in
dense linear algebra operations in inmost_dense.h

Use of memory pool for matrices in inmost_autodiff.h

Change error reporting and return type in Invert, Solve,
CholeskyInvert, CholeskySolve, PseudoInvert, PseudoSolve

Add unit tests for linear algebra on dense matrices.

thread_private class for static OpenMP objects acts as iterator

EndModification do not unnecessarily delete orphan elements

Fixed Face::getNodes behaviour inside BeginModification and
EndModification region (same fix as in andre_brench)

Added template access functions for AbstractEntry class, allows to get
(matrix of) values, unknown indices or unknowns themselves depending on
template parameter

Examples/OldDrawGrid:
* Adjustments for svg output of color gradient in color bar (previously
was not properly working in Inkscape)
* Preparations for isosurface extraction code

Possible fix in packtagdata/unpacktagdata - mismatch between amount of
calls to MPI_Pack and MPI_Unpack

GridTool for Kmeans clustering, should eventually move to Partitioner
class

Fix binary heap with key update in maximum product transversal
algorithm in inner solvers.

Correct global rescaling strategy in MLMPTILUC2 inner solver.