Attempt to restructure the controllers by using action composition
in place of the mixed in trait actions, where each concrete controller
has to override various params such as templates and the item model
constructor. This should be one way to fix the problem of putting an
implicit Lang in scope for the i18n Messages to use. Only list() and
get() actions converted yet, and I'm not sure the more complex mutation
actions will be as easily convertable.
Converted createAction to composition over mixin inheritance
Converted updating to use action composition
Completed experimental controller refactoring to use composition
instead of trait mixins. The result contains much more LOC but is
probably more customisable, less confusing, and hopefully slightly
more maintainable (if the maintainer can grok action composition.)
There is still a number of cleanups that can now be put into place,
such as making user/request/lang parameters implicit in all
templates.
Removed explicit use of user and request in templates, and added an
implicit lang. I18n now works as it should.
Plaster a flash scope all over the templates for reasons of dub-
ious validity.