Fix title rendering.
Fixed classes form
Machine name exist callback can be a class function now
Rename manage_custom path to manage_code
Converted last procedural forms to classes in the ds ui module
Remove unneeded file
Converted most of the field form callbacks to a new style controller
merged in 8.x-2.x branch
Removed last variable_set from DS
Converted the view mode delete form to a new style controller
