Allow to create arrays through GUI

[Matthias Schoettle]

Issue #94 introduced arrays to the metamodel. When the user types in the signature and types in an array as a type, the array should be created on the fly (which is taken care of by when trying to get the type, like for collections).

[Matthias Schoettle]

This was addressed with commit 99fcc8f and adf457e. We should make sure that it works well and that for attributes only arrays of primitive type can be created/used.

[Matthias Schoettle]

Works fine. Please re-open in case of any other problems.