cleaned up assembling and dirichlet BC

examples/init/stokes.dat.2d

src/amdis/CMakeLists.txt

src/amdis/DirichletBC.hpp

src/amdis/DirichletBC.inc.hpp

src/amdis/ProblemStat.hpp

src/amdis/ProblemStat.inc.hpp

src/amdis/linear_algebra/CMakeLists.txt

src/amdis/linear_algebra/Common.hpp

src/amdis/linear_algebra/DOFMatrixBase.hpp

src/amdis/linear_algebra/DOFMatrixBase.inc.hpp

src/amdis/linear_algebra/DOFVectorBase.hpp

src/amdis/linear_algebra/DOFVectorBase.inc.hpp

src/amdis/utility/TreeData.hpp

src/amdis/utility/TreePath.hpp

test/TreeDataTest.cpp