Mouth size & facial line opacity

[tomkennedy22]

This PR makes two small-ish changes. This will lead to greater variability in player faces

Line Opacity:

• This attribute is "face-wide", similar to fatness, and will apply to multiple features, including miscLines, mouthLines, eyeLines
• This attribute is applied as opacity to the three features mentioned
• The attribute is generated as random() ** 2 - meaning 0.9 ➡️ 0.81, 0.5 ➡️ 0.25, 0.1 ➡️ 0.01, and so on
• The squared random function results in a phased-in line opacity, so most lines will not be 100% opaque
  

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Mouth Sizing

• This attribute exists within mouth, and scales from 0.7 ➡️ 1.3

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Request for feedback

• Should line opacity influence whether lines appear at all? Should lines always be popualted, but not show up unless opacity > X?
• Could line opacity lead to additional aging functionality? Aging zengm-games/facesjs#3
• Is mouth range ok?
• Should mouth range "anchor" or have normal curve closed to 1?