Fix templates to match Plone 6 master template

[szakitibi]

The current @@fields, @@actions forms and the related modelleditor views fill the content slot of the master template, which is changed with Plone 6, see comment from Products.CMFPlone:

Please note that this template fills the "content" slot instead of the "main" slot, this is done so we can provide stuff like the content tabs. This also means that we have to supply things that are normally present from main_template. [source]

The model_listing.pt also inserts additional #edit-bar div and a duplicate portal message. See it on https://classic.demo.plone.org/ by creating an EasyForm, and opening the fields actions. A search for #edit-bar in the console will have multiple results. The duplicate portal message does not show up, since the master template one already dumps the messages.

The proposed changes remove the duplicate edit bar and portal messages, while updating the templates to match Plone 6 master template, while providing the things normally present in main template (e.g. article#content).

Note: The templates could be further simplified if the main slot is used, but it would add the footer and plone.belowcontent to the views.