added edge union cases

src/utilities/orientation.cpp

src/utilities/triangulation.cpp

tests/edge_union_cases.cpp

tests/quad_tree_tests.cpp

tests/union_neighbours_tests.cpp

tests/union_tests.cpp

tests/unit_tests/contourize_tests.cpp

tests/unit_tests/convex_triangulation_tests.cpp

tests/unit_tests/ear_removal_tests.cpp

tests/unit_tests/interpolate_z_tests.cpp

tests/unit_tests/orientation_tests.cpp

tests/unit_tests/split_triangle_tests.cpp

tests/unit_tests/triangulation_tests.cpp