Screen shown before the actual split.

• Is accessed with ?action=splittopics;sa=index.
• Default sub action for ?action=splittopics.
• Uses 'ask' sub template of the SplitTopics template.
• Redirects to SplitSelectTopics if the message given turns out to be the first message of a topic.
• Shows the user three ways to split the current topic.
• Same as SplitTopics1 in 1.0.x