[analytics] access labels of choices

[open-dynaMIX]

We need to be able to display the labels of options and forms (generally of all entities, that have a label), rather than just the slug.

For this, we could use similar extractors like with the DateAnswer. So we would have .slug and .label.

[open-dynaMIX]

@winged FYI

[open-dynaMIX]

This is done.