Make Form extend EntityDocument
I intentionally leave two unfinished decisions in this patch:
- Form::setId is short-circuited with an exception. I'm aware this is
awkward, but I believe this is the best we can do for now.
- I believe lists of grammatical features should also be equal if the
order is different. But this heavily depends on an other decision: is the
first grammatical feature somehow "special", e.g. in certain formatters?
The order might be relevant then. For this patch here I go with the basic
solution and consider different orders different.