Move handling of package constants entirely to SCodeInst

[Per Östlund]

Right now we use SCodeDependency to find all package constants. This doesn't quite work as intended, and introduces unnecessary dependencies between the modules. We should instead move that part to SCodeInst. We need to either go through all the classes and instantiate any package constants we find, or collect them as we go along (perhaps use the symbol table?). We also need to instantiate package constants inside components, e.g.:

model A
  package P
    constant Integer i = 0;
  end P;

  Integer x = P.i;
end A;

model B
  A a(P(i = 3));
end B;

In this case we need to instantiate a.P.i.

[Dietmar Winkler]

It doesn't make sense to keep closed ticket in the "Future" milestone that were simply forgotten to assign to the correct milestone in the past.

[Martin Sjölund]

Removing the pre1.9.4 milestone in favor of 1.9.4.