Add candidacy threads

[traumschule]

Related: #2402

I noticed that during elections a lot of communication happens on Discord that may be better saved in threads.

Similar to bounties each candidacy deserve its own thread.

Pioneer can be modified to create a thread after announcing by batching or transmitting another tx.

The candidate card should show the number of replies and on click, either

• open the thread like normal forum thread.
• open a modal displaying the candidate node followed by responses with an option to post a reply.
• expand the candidate card and expand posts below like a proposal discussion (requires to make the card expandable like for accounts)

[dmtrjsg]

Makes sense 👍 A lot of candidates already create Forum threads created to their candidacy..