fixed missing type information on related models

[joschne]

What type of pull request are you creating?

• [x ] Bug Fix
• [ ] Enhancement
• [ ] Documentation

How many unit test did you write for this pull request?

zero. small fix that runs without any problems on my big project.

Please add a description for your pull request:

Issue Related models will not be typed (i.e. get the type any or any[]) if they do not appear in a scope method (like `getrelated_model"). This leads to a lot of missing type information if you have a clean rest api, where you only expose a few remote methods but not the whole bunch of methods exposed by default.

Solution This Pull Request adds the type information about the related model to the model description.

[joschne]

Additionally I added a '?' to optional class properties in order to support this feature introduced with TypeScript 2