Limit topic creation for new accounts

[Clorith]

Spam accounts will, in most cases, start creating topic as soon as they are registered, enforcing a limit on new topics in a given time for new accounts would greatly help reduce this issue.

An expected "safe" time would be 3-5 new topics in the first 24 hours, after they reach the limit, apply the pending tag to any new threads created within that time period and flag the author.

This means we don't count posts (because they could be following up on their own issues), and it is very unlikely that a new account creates more than 3 topics in the first day, they usually want one specific issue solved, but this gives some leeway for a review or two while they're there, and any pending posts will easily be sorted out.

[SergeyBiryukov]

Related: #568

[Clorith]

In attachment:2261.patch​, new topics are checked for account age, and if it is less than 24 hours old, will put anything after the first 3 new topics in the pending view for a moderator to manually approve.

[SergeyBiryukov]

In 5605:

Support Forums: Only allow 3 published topics from a user in the first 24 hours.

If the user has exceeded their limit, move any new topics to moderation queue.

Props Clorith.
Fixes #2261.