v0.12.94: @newsroom.writer: a limit on front-page headlines

The front page shows each article's title up to its first colon. Titles whose colon came late, or never, filled the Latest list with whole paragraphs (the owner's screenshot from a phone). split_title in admin/build/front.py now caps a headline at 72 characters: it ends at a question mark inside the limit if there is one, with the rest moved to the dek, and otherwise at the last word that fits, with an ellipsis. Every headline on the front page now fits; the longest is 60 characters. The article's own title is unchanged.