Do not load tiles while interacting

Especially on mobile devices, loading just a single tile can
cause major janks. During animations, it is fine to just skip
frames. But during user interaction (e.g. dragging), a more
instant visual feedback is desirable.
Make loading parameters configurable
No typecast needed
Make the default effectively truthy
Merge pull request #1693 from ahocevar/no-load-on-interacting

Do not load tiles while interacting