Keyup events leaking

I tried to create a twiddle to demonstrate this, but wasn't able to get Twiddle to import the `ember-power-select-typeahead` addon, so I'll try to explain as best as I can.

We have a component that listens for the arrow up/down keys and reacts to those keys being pressed. Outside of that component is another one that has EPST in it. When the EPST dropdown is open and you use the arrow keys to move the highlighted item, the other component is also receiving the keyup events, which leads to some weird UI behavior.

It appears that the keyup events are not being `stopPropagation`ed, and allowed to leak out of the EPST.

EPST version: 0.6.1
Browser: Chrome 65.0.3325.181
OS: MacOS Sierra 10.12.6

Start by reproducing the issue with ember-power-select-typeahead 0.6.1 in Chrome on macOS, using an open dropdown and arrow-key navigation alongside a component that listens for arrow-key events. Trace the keyup event from the typeahead dropdown outward. Done means navigating highlighted items no longer triggers the unrelated outside component.

Written by the indexing model from the issue text.