Add a test animation
Add slider to PlayerView

Add Volume property to MediaPlayer
Add HappyHigh scale test emotion

Creates part of the Happy emotion on high intensity and applies it to
the entire string. Centres scale in the bottom middle of the textbox.
Change Animation to use keyframes

This allows the scale to start at 0.5x, go up to 1.3x, and then return
back to 1x at the end.