No need to add "*" with "auto"

Required to run macro in compiled mode

Tessellated improvements: more construction options, faster closing, reading from .obj with tutorial macro.

Relating to TGeoVector3 as Vertex_t via a single type definition file, making future switch easy. Clang formatting.

Use HTML for all kind of help messages, add more necessary checks

It is simple RWebWindow, where complete HTML code can be replaced via
communication channel. Probably such kind of widgets can be provided as
standard ROOT widget.

Provide example in webdemo.C tutorial.
Raytracing is not (yet) supported by TGeoPainter

Use it in webdemo.C example

It is replication of geodemo.C, but with web-based geometry viewer

Added GDML support for: opticalsurface, skinsurface, bordersurface, matrix, property, including test macro

Tutorials should either rely on rootmaps and remove gSystem->Load(), or use R__LOAD_LIBRARY instead.

All tutorials calling gSystem->Load() have been been revisited as suggested here https://sft.its.cern.ch/jira/browse/ROOT-8938

ClassImp is a macro defined in Rtypes.h. It can be written without trailing
semicolon. However, clang-format is based on lexing and it doesn't know at
all about preprocessors and how to expand macros. When visiting ClassImp(X)
it thinks this is not a completed entity (as it doesn't expand macros) and
considers the next line as continuation of the previous.

Inserting a semicolon fixes the issue and makes formatting with clang-format
in the ROOT codebase less tricky.

This reverts commit 5c076c6c.

This reverts commit b406328d, reversing
changes made to 318c7a47.

This reverts commit 677a3e31.

Conflicts:
	tutorials/geom/na49.C

This reverts commit 88ee63d1.

Make use of gROOT->GetTutorialsDir() to locate tutorials (currently failing for installations with prefix).

Fix issue with TGeoPainter and the new implementation of TFormula (see https://root.cern.ch/phpBB3/viewtopic.php?f=3&t=20555 ). Added geom tutorials that can run without GUI.

Fix errors with a couple of tutorials, as reported on the forum (https://root.cern.ch/phpBB3/viewtopic.php?f=3&t=19994)

Size of the library created with aclic reduced from 2.7MB
to 905KB eliminating duplicates and using functions.

Major fixes and new features for the parallel world. Declaring the physical nodes and overlaps has to be done by name. Overlaps can be automatically detected after tracking. The parallel world can be drawn.

(cherry picked from commit 9dcefdea)

Conflicts:
	geom/geom/inc/TGeoParallelWorld.h
	geom/geom/src/TGeoNavigator.cxx
	geom/geom/src/TGeoParallelWorld.cxx
	tutorials/geom/parallel_world.C