Fix bug at the domain's edges caused by incorrect neighbors

There was a bug at the edges of the fluid domain in positive coordinate direction:

For certain gird sizes the fluid nodes on the edges had invalid neighbors. To make them visible we added a function which writes the neighbors to a vtk files: NeighborDebugWriter::writeNeighborLinkLinesDebug(para.get()); There is a file for each of the 27 directions. The file contains lines which connect each node to the neighbor in the respective direction. The image below shows the neighbors in PPO-direction:

To fix this bug void GridImp::setStopperNeighborCoords(uint index) was modified:

vf::Math::lessEqual(y + delta, endY) was changed to vf::Math::lessEqual(y + delta, endY + (0.5 * delta))

The image below visualizes the new version after the bugfix: