Image selection

Removes _selectedImage.
@winhamwr regarding zero–time `setTimeout`, I highly recommend [this talk](http://youtu.be/8aGhZQkoFbQ).

In short, the browser holds a sequential stack of calls and it runs them ASAP, sequentially. When one call ends, the next can start.

`setTimeout` adds a call on top of that stack, after the specified time. A zero time means that it gets throw on that stack immediately.

In our case, when an image gets a mouse event, some various named and unnamed events occur. Amongst them is `mouseup`, which we have a handler for. In pre–7 Trident, that handler throws a selection action on top of the call queue stack, with `setTimeout` with zero time. After that, the `controlselect` is triggered and the resize handles appear. After that, synchronous code had finished running and the browser's event loop executes the next call in the queue stack, which is almost certainly the selection call which we had previously thrown there from `mouseup`.