Support new dir structure - support any dir structure, actually.

Allow THtml to find files even if they are only known as "include/TObject.h": THtml now parses all subdirs of the input path. Req by Gerhard Brandt, Fons.
Structure THtml's 1000 configuration vars a bit.
Implemented traits-like objects that allow the user to define modules, where to find files, etc, by deriving from the base classes used by THtml. 
Improve the doc search: add the top links box to all pages; add the search in there; make search ignore src/, examples/ subdirs of the output dir (i.e. only look at the doc itself) - req by Diego C.
Add info for methods' signal / menu / etc setting - req by Valeri O.
Print both last modified (source file change date) and last generated (html generation date) - suggested by Ornella.
Silence directive parser when encountering unknown directives - req by Rene.

Open issues remaining: typedef-to-class need separate page, forwarding to class's page. (req by Vassili Maroussov, Katharina Ehrhardt), TMath doc a bit broken.


git-svn-id: http://root.cern.ch/svn/root/trunk@23799 27541ba8-7e3a-0410-8455-c3a389f83636