New inspections.

Consider making a cached value of ```ErlangFileImpl#getImportedFunctions``` and overriding ```ErlangInspectionBase#checkFile``` here instead. 

The thing is ```ErlangFileImpl#getImportedFunctions``` is used in function resolution, completion and the ```ErlangDefiningImportedFunctionInspection```. Caching the value would bring a performance gain.