[MGTL] Fix calculation of search length.

In case of aquidistant meshes the expression sum_of_sqr - (sum*sum)/edge_cnt can
get negative due to numerical calculation.  The root of a negative value is not
computable in real numbers.
[MGTL] Added class MeshNodesToPoints.

It is used for conversion of mesh nodes to geometric points required for
visualization.
[MGTL] Add assertion in MeshNodesAlongPolyline().
[ML] Decrease Lis solver default tolerance.

This resolves issues for to high tolerance when applied to matrices with penalty terms from Dirichlet BC.
[ML] Using Eigen notation in GloablDenseMatrix.

Using rows() and cols() instead of getNRows() and getNCols().
[ML] Add FP_T and IDX_T typedefs for LisMatrix
[ML] Comment out matrix size check in GlobalDenseMatrix::add().
[ML] Comment out matrix size check in LisMatrix::add().
Add SimpleTest/FemTests to global cmake.
Add SimpleGroundWaterFlow cmake config.
[2dGWFlow] Add test program body that includes reading of mesh and geo.
Using read fem conditions generating mesh node ids.
Add MeshSubset.
WIP: Added some code for assembling.
Adding element constants (DIM and NPOINTS) as static variables to ShapeQuad4.
Renamed vector mesh_node_ids -> bc_mesh_node_ids.
Added includes for assembly.
[WIP] Try to implement local assembler.
[WIP] Using LocalGWAssembler in GlobalAssembler.
[WIP] Next step is applying BC to sys. of lin. eq.