Enable modeling of technology-specific enumeration types

[frademacher]

Currently, LEMMA enables the modeling of technology-specific primitive, structured, and list types. Technology-specific enumeration types are not supported. However, their integration would be sensible to express technology-specific types, e.g., in the context of Java types that have a constructor for enumeration values (cf. issue #7).

Possible syntax for technology-specific enumeration types:

technology spring {
    types {
        enum type ResponseEntity;
    }
}