Merge branch 'precompute' into develop:

- Form factors of polyhedron and polygonal prism now compute vertex positions etc
  upon call of onChange().
- ParameterPool and RealParameterWrapper now have an attribute m_parent pointing
  to an IParametrized object. When a value is set, m_parent->onChange() is called.
  This mechanism is experimental; a possible alternative, registration of lambda
  functions, may be rediscussed later.
- Parameter names of polygonal prisms and polyhedra somewhat unified: edge and
  base_edge instead of length and radius.
- Tests will be repaired or improved under issue 1294.