Remove the active_votes field from API calls to optimize front ends

this one comes from @asgarth

I would like some opinions on a change I discussed with @roadscape some time ago to the hivemind API. Basically I would like to remove the active_votes field from all the response that involve more than one post/comment (all the feeds). Or we can just leave the field there but empty. And we can use another call to fetch the vote array only when really needed.

I don't think we should change the api to do that, because a lot of applications depend on it and introducing a breaking change would hurt a lot of apps, but I think a new option to tell the api "do not send me active votes" would work well.