mypy: Clean out or report issues in mypy/typeshed for `type: ignores`

[timabbott]

Now that we've finished #127, it's worth doing a bit of work on the type: ignores in our mypy annotations, trying to fix upstream in typeshed anything where that's possible.

I don't want this issue to remain open forever, so we should happily close this as soon as we've done a sweep through our type: ignore entries.

@neiljp I feel like you'd probably be pretty effective at doing this.

[neiljp]

@zulipbot claim

[neiljp]

#157 Should cover most of this, I think?

I think I had a copy/paste issue, as the work on generate_manifest.py I intended to link to
python/mypy#1747, which was my reported issue; the corresponding PR I just worked on is python/mypy#1748.

[timabbott]

Yeah, this seems good enough for this issue (though of course you're welcome to contribute fixes upstream to clean this out further!). Thanks @neiljp!

[neiljp]

For the record, the correct links I reported and which are now fixed were in python/typeshed, not python/mypy. I'm just putting together a PR which removes these ignores and upgrades to mypy 0.560.