replace modifyParameters

• Remove functionality of actually modifying parameters, which could cause errors in connected components
  • RectBeam
• overrideParameters
  • Cutout
  • UChannel
  • Stool
  • ServoMount
  • maybe could be automatic in Component or Parameterized with a Function?
    • Maybe throw warning if both overridden and overriding parameters are set
• More complex "overrides", e.g.:
  • RightTriangle where any two of three edge lengths can be set to define the third
  • rectangular things with any two of {l, w, diagonal, perimeter, aspect ratio, area}
  • there may be other kinds of relationships
• checkParameters [ throw error if doesn't meet specs ]
  • call Parameter.assertValid()
  • probably already does that in Component.make() somewhere, but should verify
  • probably related to #4 (closed)
• Allow and check other constraints not handled by Parameter specs (a la old addSemanticConstraint construct via Functions)