Provide the «New Category» dialog with an ability to choose an existing topic as the category topic

[dmitry_fedyuk (Dmitrii Fediuk)]

Provide the «New Category» dialog with an ability to choose an existing topic as the category topic.

See also: Provide the «New Category» dialog with an ability to suppress an auto-creation of the category topic.

[sam (Sam Saffron)]

My concern here is that it would complicate the UI quite a lot for a case that is enormously rare.