Annotate widely imported modules

Most projects have some widely imported modules, such as utilities ormodel classes. It’s a good idea to annotate these pretty early on,since this allows code using these modules to be type checked moreeffectively. Since mypy supports gradual typing, it’s okay to leavesome of these modules unannotated. The more you annotate, the moreuseful mypy will be, but even a little annotation coverage is useful.