add missing includes in API for GFaceCompound and SOrientedBoundingBox

- pretty print code

set better default char length (avg of existing line ele sizes) in
addOCCMeshConstraints

never ever change the immutable vertex numbers: otherwise we cannot use
our algorithms from outside with prescribed boundary meshes

-> use MVertex::_index instead

(renamed setNum to forceNum to make sure we don't use setNum by mistake)

make Show/Hide work with GModel entities

fix warnings

make MElement and MVertex thread-safe by guarding _globalNum

add benchmark/boolean

refactor occMeshConstraints + add missing writeOCC functions

Improved reduction algorithm when generators of highest dimension are
present.
Added Betti number computation using coreduction to the UI.
Added support to quadrangles (not yet to prisms, hexaherdons or pyramids
due to unresolved issues).
Bugfixes.

levelset from postview !

add matheval levelset

more work on polyhedra

GModel::readGEO must be a static member function, since the parser can
now create multiple models!

more work on levelsets & co