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.
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.
Fixed warning type qualifiers ignored on function return type.
Fixed warning "unused variable".
Fixed warning for not initialized variable.
Merge pull request #130 from TomFischer/FixLinuxWarnings

Small pull request to fix warnings appearing when compiling with gcc 4.8.
Removed unusable constructor.

The constructor does not allocate memory. Furthermore it is not possible to allocate memory later on.
Added new class MatrixSparsityPattern.
Added constructor using MatrixSparsityPattern.
Made constructors of CRSMatrix explicit.
Replace nondependent lookup of _n_rows by dependent.