Settings: remove screen-off animation checkbox

Instead of having a separate checkbox on whether to
enable an animation, let's collapse it into the listview
preference. Now the user is presented with 3 options:

* Disabled
* Electron beam
* Fade out

Change-Id: I8bdcfbf5eba6b639eecabe22ad9b78b642f636df
Signed-off-by: Roman Birg <roman@cyngn.com>