add field type allowing autocomplete

[moritzschepp]

It depends a bit on the use case here: For simple cases, e.g. less than 50 autosuggested terms, I would suggest a preconfigured values field (#196). If there are more values, it depends where they are coming from. If this is also a static list of values, we could implement it similarly to #196 but if the ultimate goal is to query third party apis, its probably better to write specialized fields for each of them, e.g. the DNB field or the Wikidata field. @wuebbena, what do you think?