TGLPadHistpainter/TGLAxisPainter/TGLLegoPainter - new hist-painter
infrastructure.

First version of TGLLegoPainter, the new class to support different types
of legos:
gl + lego(1)/lego2 + pol/cyl/sph
gl + lego3

TGLUtil : Small auxilary classes.

IMPORTANT: this lego painter is still experimantal and works only if
it's enabled in system.rootrc. By default, TGLHistPainter is used now.
To enable this new system the line:

Plugin.TGLHistPainter: * TGLHistPainter RGL "TGLHistPainter(TH1*)"

Must be replaced with

Plugin.TGLHistPainter: * TGLPadHistPainter RGL "TGLPadHistPainter(TH1*)"

in $ROOTSYS/etc/system.rootrc


git-svn-id: http://root.cern.ch/svn/root/trunk@15406 27541ba8-7e3a-0410-8455-c3a389f83636