Fixed a problem in PiecewiseLinearInterpolation.

If the point to interpolate the value on is not located in any interval we choose either the first or the last interval and extrapolate the data. The algorithm for the determination of the interval is corrected.
Adding file converter utilities to main CMakeLists.txt.
Small changes for compilation with OGS-6.
Using Polyline::getPoint() for accessing polyline data.
Corrected include path.
Fixed include dependencies.
Fixed linker error linking Utils/FileConverter programs.
Removed unused libraries from library list for the linker.
Small changes to fix compile errors in OGS-6.
Using OGS-6 data structures to read the mesh.
Commented out most of the code.

If we need this tool in OGS-6, we have to reimplement it.
Using logog and TCLAP in ConvertSHPToGLI.cpp
Added simple program to convert OGS meshes into vtk format.