Provide option to hide paragraphs drag & drop button

Problem/Motivation

Paragraph adds the option to switch to a drag & drop mode when the core/selectable library is available. Since the default drag & drop mechanism is always available, it would be nice to decide, if that feature is displayed or not to reduce UI clutter.

Proposed resolution

Provide a widget configuration, that disables this functionality. Make the paragraphs behaviour the default setting for the option.

User interface changes

Paragraphs experimental field widget configuration has a new option to enable/disable the drag & drop button in the action menu