Reading mode hides selected text play button for TTS

The simplification provided by the Reading Mode preference will hide the play button for selected text from the text-to-speech preference. This widget should be excluded from the hiding algorithm.

Steps to reproduce:

1. Launch chrome with the UIO+ extension running
2. Open UIO+ and enable text-to-speech
3. Select some text. The "Play" button should be showing over the selected text.
4. Open UIO+ again and enable reading mode
   1. Notice that the play button is hidden.