Volume quadratic and volume steps of 10.

[iHD992]

Similar to "Simple gamma correction for display#293" but for sound.

Description

This PR improves the sound experience by addressing the non-linear nature of human volume perception.

Changes:

• Volume is still giving in percent, but the value is squared and divided by 100. Thus the user can do fines changes at low volumes and at high volumes changes still have an impact.
• The intervals are steps of 10 %. Seems sufficient and 5 % would complicate things as audio.volume is an int, not a float.