1.) Layout initialization logic for fo:table, fo:table-header, and fo:table-footer

1.) Layout initialization logic for fo:table, fo:table-header, and fo:table-footer
moved from AddLMVisitor to fo.Table.

2.) Layout logic for fo:external-graphic moved from fo.ExternalGraphic to
layoutmgr.ExternalGraphicLayoutManager.

3.) Partial implementation of validateChildNode() for fo:footnote.

4.) fox:destination commented out from images.fo sample until purpose, content
model better defined.  Also needs a Maker class.  (Does not appear to work
in either maintenance or HEAD.)

git-svn-id: https://svn.apache.org/repos/asf/xmlgraphics/fop/trunk@197867 13f79535-47bb-0310-9956-ffa450edef68