Automate / infer decisions for corpus definitions

[lukavdplas]

At the moment, there are many points where a corpus definitions offers a choice where in fact there is none, such as the type of filter for a particular field. To make the menu more user-friendly, such decisions should be inferred whenever possible.

[lukavdplas]

This is largely covered by the JSON API (#1519), which makes a lot of these inferences. There are only a few minor points where they JSON schema still offers an "illusion of choice" (for instance, whether an integer field should have full-text search enabled), but this will be covered in #982. No need to track this as a separate issue anymore.