Spacebar plays audio of highlighted unit

[johnwdubois]

Let the user play the audio of the currently highlighted unit by pressing the spacebar.

1. In the main screen, the user hovers over the empty space the right of a line of text.
   • This line should be highlighted in some way (e.g. light grey background)
2. When the user presses the spacebar:
   • begin playing audio from the startTime of the highlighted unit

Screenshot

See line 1759 (sbc006)" "Supposedly Alina's been on this diet"

[johnwdubois]

There is an echo when playing the beginning of a line. (The beginning plays twice.) It should be eliminated.