Using java annotations instead of scala type aliases does not work

Using java annotations directly has no effect.
One have to use the scala type aliases.

Ex:
```
import io.sphere.mongo.generic.annotations.MongoKey
case class Student(
@MongoKey("_id") id: String
)
```
does not work.

The following works
```
import io.sphere.mongo.generic.MongoKey
case class Student(
@MongoKey("_id") id: String
)
```

Start by reproducing the issue with the two Student examples and compare the MongoKey definitions behind the import paths shown in the report. Trace annotation handling for the Java annotation versus the Scala type alias; done means the Java annotation directly on the case-class field has the same effect as the Scala alias.

Written by the indexing model from the issue text.