Merge branch 'feature/linear-systems' into 'develop'

src/algebra/BiCGStab.hpp

src/algebra/CRSMatrix.hpp

src/algebra/PCG.hpp

src/algebra/SparseMatrixDescriptor.hpp

src/algebra/Vector.hpp

tests/CMakeLists.txt

tests/test_BiCGStab.cpp

tests/test_CRSMatrix.cpp

tests/test_PCG.cpp

tests/test_SparseMatrixDescriptor.cpp

tests/test_Vector.cpp

tests/test_main.cpp