[bug 1094197] Fix JSONObjectField default default

This fixes the default so that it's always u'{}'. It can be overridden,
so mostly this just codifies the default so we don't have to keep typing
it across the codebase.
Merge pull request #376 from willkg/1094197-fix-jsonobjectfield

[bug 1094197] Fix JSONObjectField default default
Tweak chart display
Add xx to DEV_LANGUAGES and tweak documentation

* add the xx locale to DEV_LANGUAGES since it reduces some of the steps
  involved in testing string localization
* tweak locale.py-dist documentation to improve it and point to detailed
  documentation
Update docs regarding the xx locale
Make journal.Record not derive from ModelBase

This model overrides objects, so there's no reason it should derive from
ModelBase. This fixes that.