Provide ability to configure 'show summary in full view' node setting

When adding or editing a node, it is possible to enable or disable a checkbox "show summary in full view". This determines whether the teaser entered is displayed on the full node page and defaults to true. I have a content type in my source CMS where this should be set to false.

The attached patch adds a new field to the node content set configuration form, and also inserts the necessary <!--break--> at the start of the node body when the option is disabled, so as to avoid editing problems later.

Cheers,
Stella