Change how sub-tabs work for a TabbedDisplayPane

Currently a sub-tab shows up to n VersesPerTab. In some cases this is too arbitrary a boundary.

Consider the following (assuming 50 verses per tab):

• There are 51 verses to show. In this case another tab is a nuisance.
• There are 80 verses to show, but it the chapter boundary is really close to 50 verses (say 45 or 55). It would make more sense to split on a chapter boundary.
• The user has selected to view 5 chapters. It would make more sense to view one chapter per tab or maybe 2 tabs for a really big chapter.

Basically we should sense whether the user is in arbitrary verse mode (e.g. search) or in chapter mode (e.g. lookup) and either show chapters per tab (possibly overflowing to a second tab, if there are almost 2n verses in the chapter) or n verses per tab with widow/orphan control of a few verses (say 5).