corrected some bugs in 2d mesher & occ interface

- save physicals labels when saving unrolled geometries
- fixed crash in unrolled geo save (discrete points)
- Delete Physicals now also deletes the physicals in GModel
- removed unused rules and terminals in parser
- put at least one mid-point when meshing non-straight lines
  in OCC: this fixes most of the trivial 2d meshing problems

removed most unused, untested or non-working stuff in old CAD code

- bug fix: need to create temporary bounding box and compute CTX.lc
*during* parsing step until we fill the new db on the fly

(Some geo transforms in the parser use CTX.lc for tolerences. But
CTX.lc was always equal to 1 since we only do a SetBoundingBox on
GModel after parsing!)

- cleanup spline interpol (remove duplicate code)

OpenProblem -> OpenProject
MergeProblem -> MergeFile

Layers{N,1} can now be written simply as Layers{N}

deprecated -> warnings instead of errors

make default transfinite subdivision match old version to minimize
backward compat problems

new option to compute char lengths from curvature + removed most unused mesh options

curvature control is ok
divide and conquer algo has been cleaned up

more infrastructure for projection face gui

physical entities can now be defined using a string instead of a number (and
there is a new field $PhysicalNames in the .msh format to keep track of these
strings)

remove elliptic - same as Transfinite with Mesh.Smoothing > 1

- finished volume extrusion
- cleanup ExtrudeParam (plug memory leak + remove unused stuff)
- make netgen the default 3D algo for now (since it actually works)

make explicit regions in extrusions DEPRECATED

cleanup

bidir db: phase 3 -- move all the old geo stuff into Geo/

bidi db: phase 2 -- continued

bidir db: phase 2 -- removed all (well, most of) the old data structures and
algorithms

bidir db: phase 1

- add compatibility syntax for getdp (string~{fexpr})
- add possibility to write/append to files with Printf

merging offscreen rendering from branch

- fix discrete surf (for the 100000th time)
- new Status N command in parser to force mesh status
- create reverse discrete curves

minimize the number of files that include GmshVersion.h: it's annoying to
recompiletoo many files just because the version string changes

moved most OS-dependent functions in OS.cpp