[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.