Streamline the selection of elements to be loaded into models

[petrsvihlik]

Blocked by: #35

Motivation

Currently, the developer needs to name elements that should be loaded from KC. If the data is used at multiple places, it's hard to keep track of what needs to be included in the model at which place.
We'd like to come up with a way of defining elements that are necessary to successfully render a view.

Design guidelines

An idea was to use the (view)models as the source of truth.

There should be a way to construct ElementsParameter just by providing a viewmodel.

[petrsvihlik]

doesn't make much sense now