Simplify the tracking of library dependencies - move them into new TLibraryDocInfo

Allow invocation of all graphjviz tools, e.g. fdp.
library dependencies: use fdp, cleaner layout by skipping A->C if A->B->C exists, too.


git-svn-id: http://root.cern.ch/svn/root/trunk@19221 27541ba8-7e3a-0410-8455-c3a389f83636