RoboCert-level constants?

[MattWindsor91]

It may be useful, for some situations, to allow the user to define a SpecificationGroup as parametric on constants that don't exist at the RoboChart level. These would then be treated the same as RoboChart constants for instantiatio npurposes.

Implementation-wise: This would require a more sophisticated scope resolution, as our current notion of 'constant = robochart, variable = robocert' would fail, as would the construction of parameterisations.

(This is actually the right repo now. Oops.)

[MattWindsor91]

This was mentioned again by Ana earlier, in regards removing a WFC that forbids constants at the lifeline level.