[UX] Layout templates are always enabled/available - so say "show"/"hide" instead of "enable"/"disable"

[klonos]

What the "Disable" action in admin/structure/layouts/settings actually does is to hide a template from the list of available templates when choosing a template in the layout create/edit form.

While at it, do we really need the "enable"/"disable" buttons in that page when we already have the checkboxes and the submit button at the bottom of the form? Should we reserve the horizontal space the buttons take for something useful instead? (like a column listing which layouts a template is being used in - separate issue than this)