Revive work on Polymorphic Sorts

[wadoon]

Introducing Sorts with Sort-Parameters.

Type of pull request

• X New feature (non-breaking change which adds functionality)
• X Breaking change (fix or feature that would cause existing functionality to change)
• X There are changes to the (Java) code
• X There are changes to the taclet rule base

[wadoon]

Support for data types:

\sorts{\generic E;} \datatypes { List<[E]> = Nil | Cons(E obj, List<[E]> tail);

Test case fails.

[mattulbrich]

There are a number of fundamental questions to be sorted out: https://github.com/KeYProject/key/wiki/Polymorphic-types-in-KeY