Applied owner and hidable to bookmark

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Change attribute name; updated_datetime to last_modified

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Change permission class IsAuthenticated to IsAuthenticatedOrReadOnly

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>