Reduce overloading of word 'index'
It would be nice if we could reduce the overloaded meaning of the word
index in Silva. Right now we have a number of meanings:
* index document in folders, which provide default view behavior for
folders. This one is the main concept to be renamed to something else if
we come up with a good name.
* Index elements inside Silva documents. These are the ones picked up by
docma for creation of 'back of the book' indexes and by the indexer in
Silva which does the same. I'm not sure how we could rename these,
as after all this thing is called an index.
* Catalog indexes. We can't really rename these as the Zope UI calls
them this way and is not particularly prone to change. Of course the
Silva user is not exposed to this but can still lead to occasional
among developers, which we'd prefer to avoid.