Various "unresolved" messages when generating the metamodel

The Transcript in Pharo has the following messages when `FamixTypeScriptGenerator generate` is executed:

```
unresolved>>metamodel (FamixTypeScriptModel is Undeclared)
unresolved>>importingContextClass (FamixTypeScriptImportingContext is Undeclared)
unresolved>>importedMetamodel (FamixTypeScriptModel is Undeclared)
```
