16b03 type fixes

Building a comprehensive PLT for R16B03 warns about the following unknown types:

```
  gen_sctp:open_option/0
  inet:ipaddress/0
  proplists:proplists/0
  public_key:private_key/0
```

This branch fixes all but the gen_sctp:open_option/0 warning, because I wasn't sure about the right approach. I'll leave that as an excercise for Raimo and Anders :-).