[ticket/12345] Improve search flood interval message for ascraeus

Show to guests and users the remaining seconds until their next allowed
search, if a search flood limit is enabled for them.

PHPBB3-12345
Merge pull request #2243 from n-aleha/ticket/12345

[ticket/12345] Improve search flood interval message for ascraeus

* n-aleha/ticket/12345:
  [ticket/12345] Improve search flood interval message for ascraeus