Improved animations for RSSNOw. While scrolling, the old item now also slides away, making it clearer that the item has just switched.

Also, only 1 timeline is now used per scroller which reduces stuttering while scrolling fast.

Quickly scrolling now also accelerates the speed at which items scroll by.

I'm still going to add a way for scrollers to delay their clearUnusedItems() to a moment where no scrollers are animated to improve animation performance further.

Also a couple of unrelated small fixes.