Add backspace to emoji drawer (+ two tiny tweaks)

Thought this would be useful, and someone was even generous enough to leave unused drawables for the purpose:

![Screenshot](https://cloud.githubusercontent.com/assets/124223/3757758/0d3b21ec-183d-11e4-9774-7b06a061076b.png)

Also two other small tweaks. (I personally think it's better without the gray placeholder squares, but that's just my opinion, man.)