[MathLib] Remove unused code.
[MathLib] Moved LU decomp. to separate method.
[MathLib] Move performLU() from constructor to solve().

In the current workflow the solver obj will be created when the matrix isn't.
For this reason the LU decomposition has to be moved to a later point in time.
[T] Using new interface of class GaussAlgorithm.
[GeoLib] Using new interface of class GaussAlgorithm.
[SimpleTests] Using new interface of class GaussAlgorithm.
Merge pull request #544 from TomFischer/LU-Problem

Correct usage of the DenseMatrix GaussAlgorithm.
[U] Init. impl. of tool for creating BCs from ply.
[FileIO] Impl. BoostXmlGmlInterface::write().

Needed for debugging and utils.
[U] Impl. of writeBCsandGML.
[U] Save each geometry set in own data set.
[U] Merge all geometry sets.
[U] Write BCs and geometry set.
[U] Get only surface nodes.

Sort the merged nodes lexicographically to obtain the surface nodes.
[U] Keep the point names.

Keep the point names deploying PointWithID and name search.
[GL] Using std::lib functions.
[GL] Remove unused var cnt.
[U] Give some progress information.
[U] Better names for readability.
[U] Reworked mesh node search algorithm.

Use the surface mesh instead of the subsurface mesh to find mesh nodes at the top.