feat: Inline-editing capability for frontend-editable models

[fsbraun]

Features

• Inline editor for CharField (no-frills)
• Auto-detection of inline-editable fields (HTMLFormField and CharField) in both models and plugins
• Enable inline-editing for models that support {% render_model instance "field_name" "field_name" %} command (renders the named field of the instance and opens an editor with only this field in the frontend) available since django CMS 3.0 - requires their admin to have the FrontendEditableAdmin mixin

Fixes

• HTML editor size in modals of text plugin
• Made URL target selection available in HTMLFields
• Balloon toolbar (for block commands, typically positioned left of the current editing line) now allows for scrolling

Issues

• Only available in edit mode which for django CMS 4+ only exists for models that register with django CMS core as frontend-editable in their app's cms_config.py

Example

Here's inline-editing for a djangocms-blog object (not using plugins but the post_text model field):