The type selection dialog should be skipped when only one
component type is declared as available for an area. As the user has
no choice at all (= only one choice to choose from), the type
selection is rather unnecessary (and somehow user-unfriendly, because
it requires an additional click).

Here's an example (type "list" is used by intention,
because several exampleComponents should be addable):

• templates
• - pages
• - - examplePage
• - - - areas
• - - - - main
• - - - - - availableComponents
• - - - - - - exampleContent
• - - - - - type
• - - - - - - list

It should be possible to add several new "exampleContents" to an examplePage without
the "Select a type for the new component" dialog showing up.