TemplateConfig implementation with Kubernetes

Initial implementation of TemplateConfig REST endpoint.

See the project.json example.

To test this PR:

```
$ curl -d @pkg/template/examples/project.json \
  http://localhost:8080/api/v1beta1/templateConfigs
```

This will return `Config{}` which is essentially the same as a `templateConfig{}` but without parameters.

**FYI**: This is a wip, all commits will be squashed in the end. @VojtechVitek is working on validation atm. so I don't want to force push ;-)
Could you be more specific? Should this validation happen during the json `Decode()` rather than on resource `Create()` on the server side? Should this code be reusable for the client validation as well (before sending to server)?

I tried creating a TemplateConfig with Item having an invalid `"kind"` field, and it seems like no runtime error occurred at all. The item was just silently ignored.

Did you mean revisiting validation upstream as well?