Replace EditorClass module with a DSL method
Create global async setting

Change `publishing_method` to `background_mode` so that it can control
method of field updating as well as publishing.
Re-jig field module naming

Rename the 'FieldType' module to just 'Field'
and remove the 'Field' suffix from the type
implementations.
Async mechanism in place

Only piece missing is the CLI command that will do the actual updating.
Use new class names for field types
Make Box#id properly identify a box instance
Correct namespace for Simultaneous
Give fields IDs

And provide a way to resolve a field from an id
Ensure that async fields' pending values are saved
CLI task for async field updating

The last piece in the puzzle
Remove use of Fibers

They just broke things anyway
Make form send values rather than a hash to the app
Run tasks from site root
Update UI to work with async image fields

- Show pending value if it exists
- Pending value has src, width & height values
- Add a new __ui__ size by default to avoid having to load full-size
images in CMS view
Update serialisation test to include new UI image size
Provide convenience Immediate.process method
Revert to Immediate updating in case of error

Probably because the Simultaneous server isn't running
Refactor server task

Rename the 'publish' task to 'tasks'
Use process method inside updater
Change fail to skip

Because it's driving me mad