ConstantName and ConstantValue should not be in PartsMenu

[c3d]

The PartsMenu contains ConstantName and ConstantValue, but there is no real good use for these in a menu. They are supposed to be interactive commands injected automatically in the constant menu, which show the constant name and value.

That being said, they should have a useful behaviour when invoked non-interactively, i.e. not from a menu. ConstantName could return the name associated with a constant (i.e. turn Ⓒre into re), and ConstantValue return the value (i.e. turn Ⓒre into 2.81794 03205 fm).

#1574 shows that they are very confusing in that spot.