Create separate `Titled` mixin for `title` attribute

* Previously, it was within `Slugged`, but sometimes one is unwanted
Add methods for model registration
Add missing copyright header
Add `GGRC.extensions` and use it for `infer_object_type`

* Basically, each extension with client-side content should register in
  the `GGRC.extensions` list.  Currently only `init_widgets` and
  `object_type_decision_tree` are supported methods.
Move ListLoader shorthand functions to `GGRC.MapperHelpers`

* This is cleaner and will enable reuse in extensions
Add models, migration, and settings for ggrc_workflows
Add initial javascript models, extensions, and templates
Remove cruft from previous commits
Make `ggrc_workflows.settings.development` a default module

* Add `ggrc_workflows.settings.development` to `GGRC_SETTINGS_MODULE`
  in `init_env` and default deployment settings
Merge pull request #1391 from reciprocity/feature/initial-workflow-extension

Initial workflow extension, models, and assets