Add post queue

[tupini07]

I was thinking it would be cool to have something like Tumblr's post queue. You basically add posts to this queue and they're automatically posted respecting a user defined cadence (for example, post 1 post from queue every day between 7am and 2pm).

Tusky's current 'schedule' functionality is really cool, but sometimes I would just want to have an automatic queue and not worry about scheduling the posts manually.

Also, here we're talking about a queue for new posts, but it could also be used to queue 'boosts'.