Embed module dependency graph in Doxygen docs

The module dependency graph generated by the dep-graphs target is now
embedded into the Doxygen documentation as a separate page (in the lib
and full variants).  Building these flavors of documentation now
requires the depgraphs to be built first, which in turn depends on the
doxygen XML output.  Added various -fast targets that skip these
dependencies, with the cost of potentially producing some warnings about
missing stuff.

Change-Id: Id3314c598d79588c429fe57108349edf42de3b6b