Grapher redesign: Add feedback for empty search result in entity selector

[sophiamersmann]

Add feedback message when no entities could be found on search in the entity selector modal.

• The message is: Nothing turned up. You may want to try using different keywords or checking for typos."
• A more specific message is displayed when the search input is an actual country (and the entities are country-like): There is no data for the country, region or group you are looking for.