Only call `remoteFetch` when vertically scrolling.

There's no mechanism to fetch more _columns_, so it doesn't make sense
to trigger remote fetches when horizontally scrolling. Fixes #122.
Include scroll distances in event in scrollTo.
Update tests to reflect new viewportchanged args.
Rename `vScrollDist` and `hScrollDist` variables.
Merge pull request #167 from mminer/prevent-fetch-on-vscroll

Prevent remoteFetch during horizontal scroll