CollectionView needs to support different templates for different types of children

[Henri Bergius]

The current assumption in VIE's CollectionView is that each collection only has one type of child elements. However, many CMSs allow you to have multiple child types. For example, in TYPO3 you could have a text element or a video.

Each of these need different templates, so we cannot just rely on using :first-child as entity template.