Add types to make the code more robust

[flensrocker]

Let TypeScript help us to pass around the right arguments to our functions.

Not handled yet: the Error type in dynamic-reactive-form.model.ts

For me it's not yet clear how this should work together with ngxErrors and ngxError. My guess is, that Validtors[] is not the right type for that. Someone with more knowledge about @ngspot/ngx-errors should take a look at that.