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.

Also rename the boundary conditions container and
remove unused BoundaryConditionsConstIterator.

For square_1x1: left Dirichlet, bottom Neumann.
For cube_1x1x1: left Dirichlet, bottom and front Neumann.

GeoLib fix line segment intersection algorithm

If two line segments are parallel, but do not intersect each other is handled now correct.

This fixes #661.