Change mission lists items' drawable when Trash icon selected/deselected

Closes https://github.com/DroidPlanner/droidplanner/issues/508

TODO:
- [ ] Fix drawable size


![screenshot_2014-07-31-13-48-47](https://cloud.githubusercontent.com/assets/3159171/3763967/af220346-18aa-11e4-96aa-4666ff5a9e90.png)
![screenshot_2014-07-31-13-48-51](https://cloud.githubusercontent.com/assets/3159171/3763968/af3f20fc-18aa-11e4-8161-b430582c19da.png)
@arthurbenemann the code is correct, otherwise as the device rotates (orientation change) the editor will lose the state it's currently in.