Reduce complexity of Claims class

In an attempt to reduce the complexity of this class I found that `append` is not necessary. `append` calls `offsetSet` which does the same type check again. I added a test to make sure the type check is not lost.

The change to `$arrayObject[] = $element` does have the same reason. The `[] =` is just an other way to `append` but does _not_ call `append` internally. Instead it calls `offsetSet` directly. Which is what I want.