add eyebrows

[albertochiwas]

Inside AvatarFace Tab:

• Derive a MonsterEyebrow from AnimatedFeature class, very similar to MonsterEye
• Define constructor for MonsterEyebrow class, call close() by default (eyebrows down).
• Define open()& close() methods for MonsterEyebrow, to create up & down eyebrows shapes.
• Add leftBrow& rightBrow attributes to AvatarFace class.
• Initialize leftBrow& rightBrow attributes inside AvatarFace constructor.

[albertochiwas]

15-30 min. story