Parse new-expression

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Elaboration tests

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add return-monad

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>
Add model instantiation elaboration

Signed-off-by: Christoph Höger <christoph.hoeger@tu-berlin.de>