Add ComposerVectorGridFunction a composer of a vector of gridfunctions

amdis/gridfunctions/CMakeLists.txt

amdis/gridfunctions/ComposerVectorGridFunction.hpp

amdis/gridfunctions/test/CMakeLists.txt

amdis/gridfunctions/test/ComposerVectorGridFunction.cpp

amdis/gridfunctions/test/CoordGridFunction.cpp

amdis/operations/Basic.hpp