tag: add {{Split}} and {{Split dab}}

[NovemLinguae]

Requested by Beeblebrox at https://en.wikipedia.org/wiki/Wikipedia_talk:Twinkle#propose_splitting%3F

• add {{Split}} to tag module
• add {{Split dab}} to tag module

There exists a tag filter called disambiguationPagesOnly, but it checks for "_(disambiguation)" at the end of the page name, so I don't think it'd cover every disambiguation page. So let's not worry about that for this patch.