Size category width dynamically

In case all the category names are short, this leaves more room for the result text.

To reduce jumpiness of the UI, the category width is only reset when clearing the query. As a result, sometimes you still get a wide category column when you e.g. had a transient "Recently used file" result earlier in your query

This also changes the logic slightly to have the category label be always categoryWidth in size. Before it would subtract gridUnit from it. Should this new behavior be exposed in a property?

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@alex

Before

After

Imho we should switch to a small spacing between category and label, because sometimes you get something awkward like this