Properties replacement method

Adds a possibility to replace properties inherited from base types with
a more specific ones. For example, such properties may have:

- different meaning which should be reflected in property name
  (e.g. TRACK::{G,S}etWidth() sets actual track width, but
  VIA::{G,S}etWidth() modifies the diameter)

- different set of possible values (e.g. BOARD_CONNECTED_ITEM::SetLayer()
  should accept any copper layer, but MODULE::SetLayer() works only with
  F.Cu and B.Cu)