generalised Laplace equation with anisotropic conductivity

Implementation the generalised Laplace equation with anisotropic conductivity - possibility to have a completely filled symmetric conductivity tensor (6 entries in 3D) and rotate from fibre coordinate system to local coordinates.
Tested in 2D against the analytical solution from Chris Bradlay.
In 3D performed tests and compared to other codes.
The code also contains pieces for the extracellular Bidomain equation - Poisson problem - which runs but is not completely finished yet.