Provide proper thumbnail url in search

[tobiasKaminsky]

http://localhost/nc/ocs/v2.php/search/providers/deck/search

does not provide thumbnailUrl, but it could show a correct preview of the note.

[juliusknorr]

Not sure how feasible a preview is, especially considering the size that the text may have in the search results and that would require custom preview generation and an extra endpoint in deck.

Since deck does not provide a thumbnail URL the web falls back to the icon, but that is indeed not working as we return a css class there (similar how it is done in mail for example). Returning an image url for the icon is possible but would break dark theme then.

@skjnldsv @ChristophWurst Should we maybe introduce a separate iconUrl field in the server search results, so that the clients can also make use of the icon fallback if no thumbnail is present?

[stefan-niedermann]

Maybe one should not try to generate a preview of the card description on title (which would be indeed a bit hard to read). But one could check whether an image is attached and display this and fall back to a generic deck icon?

[juliusknorr]

Might relate to #2858 then as well