Made CMake include paths relative.

Replace CMAKE_SOURCE_DIR with CMAKE_CURRENT_SOURCE_DIR and
CMAKE_BINARY_DIR with CMAKE_CURRENT_BINARY_DIR. This allows to use
OGS as a subdirectory in another project.
Moved class MeshCoarsener to MeshLib/MeshEditing.
Moved Mesh2MeshPropertyInterpol to MeshEditing.
Moved ConvertRasterToMesh to MeshEditing.
Moved MeshGenerator to MeshEditing.
Updated submodule paths.
Moved some classes from folder MeshEditing to folder MeshGenerators.
On Windows static Boost libs are searched for.

As long as dynamically linking is not working on Windows we should not
try to do it.
Merge pull request #119 from TomFischer/RestructureMeshLibFiles

Restructure mesh lib files.
Merge pull request #128 from bilke/Relative_CMake_Paths

Made CMake include paths relative.