Cleanup on the DOM/SC interface

Try to avoid excessive thunking between twine and JS by keeping the interface a bit cleaner.

Primarily:

• Prefer <<includeDOM>> over other methods for including DOM results in twine files (and remove App.UI.DOM.includeDOM entirely, since it's only purpose is to include DOM in Twine code that is being returned as text from Javascript functions, and we should be avoiding that situation altogether).
• Prefer App.UI.DOM.renderPassage over other methods for including Sugarcube markup in DOM, especially $(element).wiki('<<include "Passage">>') which has invokes an extra parse.