4teamwork/ftw.book#45 adapt ILatexLayout rather than Interface

Adapting to Interface for the layout seems to be too generic. It takes
precedence over namespace adapters such as ++add++ for example:

>>> ttool = getToolByName(self.context, 'portal_types')
>>> ti = ttool.getTypeInfo("Image")
>>> queryMultiAdapter((self.context, self.request, ti))
<ftw.book.latex.chapter.ChapterLaTeXView object at 0x7f9e32c089d0>

(cherry picked from commit 1474162630cad86fe0fd564027b664da4b1a9c17)