Make removal of queued items undoable

When scrolling the list in the `OrganizeQueueActivity`, items can easily be removed from the list by accident (this happened to me several times). And, if your queue is pretty full, it can be difficult to find those items in order to add them back.

This branch adds an UndoBar like the one from the official GMail app based on Roman Nurik's [UndoBar](https://plus.google.com/u/0/+RomanNurik/posts/RA9WEEGWYp6).

One problem with this implementation could be that in response to the removal of the item, the `FeedManager` might delete the item's media and start auto-downloading new episodes. These actions can currently not be undone. Maybe it would make sense to just remove the item and schedule the cleanup and auto-download for when the user leaves the activity.