Stick default formats on global enums
Remove Persistable.toJson in favour of using generics in the DAOs for Json serialising
Moving (slowly) towards selectable JSON formats.
With due trepidation, create a type class Convertable for holding
various formats.

Implementations are implicit on the model companion objects.

Currently, the REST format is the only one available, but this should
be joined by a 'client' format soon.
Add a 'client format' converter to all models, which points to the
compiler generated JSON format.
Increase parallism factor
Basic (almost) working implementation of meta models which can be
serialized in a client-friendly format.
Alter models + form/json deserialization so that the type enum is
a parameter field. This means it is visible in the default JSON
serialization.
Add more meta models
Mid refactoring, basic machinery in place for exposing a 'client'
format Json for meta-models in a generic manner. Lots of work still
to do in making it neater and more comprehensible.
Tweak error handling
Merge branch 'master' into nested_meta_model for
added 'abstract' field.

Conflicts:
	app/models/DocumentaryUnitDescription.scala
JSON tweaks
Do meta model client formatting manually, because that allows us to
put the model fields at the top level, which is clearer. It's not too
much extra typing either, since the meta models have few fields.
Fix address deserialization
Started elaborating the structure of the metamodel with base traits
Mid way through trying to refactor app to use type-safe JSON parsing
and getting rid of the unfortunate 'psuedo' wrapper types based on
the Entity model. Lots of challenges still to overcome, and this might
not actually lead to a working app.
Another big refactoring, still not compiling...
A billion more fixes on the way to getting it to compile again.
Ten million more fixes on the way to a working build...