Probably doomed attempt to decouple parsing of 'any' model to its
correct type by creating a mutable type registry for the AnyModel
object that implementing types can use. This is to permit moving the
base model code the to core module. Probably a better way is to
specify a particular AnyModel reads/format at the point of use, rather
than relying on the implicit Converter on the object itself. Yes, this
is definitely the way to go...
Different approach: try and parse/write unknown entities as plain
'Entity' type. This is less safe, but potentially lets decoupled apps
work without knowledge of all the available entity types. However, it
seems to reveal a bug in the server somewhere. TODO: fix.
Update to Play 2.1.2
Handle JSON read/format registry through Global object
Move lots of stuff to core module.

This includes the base models, user/group/link/annotation models, and
their associated JSON and form serializers. So far no additional package
renaming, so things more or less work how they did before. However, there
has been another extensive refactoring of how JSON formats are found, with
an emphasis on a) making it work, b) decoupling things, and c) reducing the
user of implicits and lazy vals.