Magic UV: Fix error raised at UserPreferences and remove legacy codes.

uv_magic_uv/__init__.py

uv_magic_uv/common.py

uv_magic_uv/impl/__init__.py

uv_magic_uv/impl/align_uv_cursor_impl.py

uv_magic_uv/impl/align_uv_impl.py

uv_magic_uv/impl/copy_paste_uv_impl.py

uv_magic_uv/impl/copy_paste_uv_uvedit_impl.py

uv_magic_uv/impl/flip_rotate_impl.py

uv_magic_uv/impl/mirror_uv_impl.py

uv_magic_uv/impl/move_uv_impl.py

uv_magic_uv/impl/pack_uv_impl.py

uv_magic_uv/impl/preserve_uv_aspect_impl.py

uv_magic_uv/impl/select_uv_impl.py

uv_magic_uv/impl/smooth_uv_impl.py

uv_magic_uv/impl/texture_lock_impl.py

uv_magic_uv/impl/texture_projection_impl.py

uv_magic_uv/impl/texture_wrap_impl.py

uv_magic_uv/impl/transfer_uv_impl.py

uv_magic_uv/impl/unwrap_constraint_impl.py

uv_magic_uv/impl/uv_bounding_box_impl.py