Generate product doc, re-group code for re-use in module/product doc

Add all gEnv configs also as setters/getters; use gEnv in THtml c'tor, afterwards only getters
write search link on each page
shorten the class inh dot diagrams for complex hierarchies
Allow trailing stuff in ViewCVS link
remove spurious empty lines in directive output
fix latex column chopping (one char missing at end)
Rename a few internal funcs
Create unique directive output GIFs
update THtml doc
Add special handling for smatrix "source" dir
Skip empty sourceinfos (author,...) in footer


git-svn-id: http://root.cern.ch/svn/root/trunk@17971 27541ba8-7e3a-0410-8455-c3a389f83636