Speaker/volume icon should be mirrored for RTL

[chrisgarrity]

I've flipped back and forth on which icons should be mirrored and which shouldn't (e.g. paintbrush)

The 'speaker' icon should be mirrored everywhere that it's used (for reference: https://material.io/design/usability/bidirectionality.html#mirroring-elements)

• sound tab
• sound library
• sound selector
• louder/softer in the effects (sound editor)