feat(middleware): allow middleware to handle muted setter/getter

[gjanblaszczyk]

Description

Allow middleware to handle muted setter and getter. This supports things like muting the media programmatically, without affecting the player's UI muted button control.

Specific Changes proposed

Add muted setter and getter to the lists of allowed Getters and Setters in the middleware feature.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors