[Fix] Added checks for VTU reader

Using new interface of Mesh to access Properties and PropertyVector in class MeshRevision

Command line tool for mapping geometry to the surface of a mesh

reduceElement returns the number of elements the given element is reduces to.

The number of new cells is used later on.

Using new mesh interface for Properties in class ElementValueModification 

Small interface change class PropertyVector

The method size() returns now the number of tuples instead of the number of values.

ElementValueModification::setByElementType() uses the new Property data structures.

Method will substitute getMeshValues() later on.

Neumann type boundary conditions.

Create boundary conditions along polyline

The solution is given in http://docs.opengeosys.org/docs/benchmarks/elliptic/groundwater-flow-neumann.

This should go into the project description really.

The Neumann BC is a*du/dn = g_N(x), and the user
provides only the g_N(x) function.