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

allow unconstrained background meshes

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

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

remove obsolete BGM structure

better export mesh as post-pro view

polish

- better fallback when outside the octree
- disable bgm when optimizing in netgen

Rewrote the background mesh code to use the new post-pro octree instead
of the old brick stuff. It's 100x faster ;-)

make the bgmesh work with quads

- new button under the graphic window to temporarily disable mouse
  selection (speeds-up redrawing of very large models + permits to
  rotate/zoom-in a model in selection mode even when the whole screen
  is full of selectable entities--e.g. a surface mesh)

- new "lasso" selection mode (to select entities using the same kind
  of lasso as the lasso zoom: just Ctrl+click, then drag the mouse in
  selection mode; the shortcuts are the same as for the lasso zoom)

- it is now possible to unselect entities using the middle mouse button
  (only for the creation of physicals at the moment; not sure if it's
  useful in the other cases)

- new button in visibility browser to invert the current selection
  (very useful e.g. when multiple physical entities are associated
  with a given elementary entity, in order to "peel" away the model
  when adding new physicals; cf. philou)

- changed meaning of Escape shortcut (cancel lasso or toggle mouse
  selection) + restore standard fltk Escape handling for all dialog
  windows

- updated copyright string

- new mesh label mode (coordinates); all label types are now also
  available for mesh vertices

- added option in 'Print Option' dialog to disable printing of help
  strings

- added a comment string with the date when creating a new file

- new snapping grid for adding points in the GUI

replaced ExportLCField with ExportMeshStatistics (lc + gamma, eta, rho + elem num)

copyright update

optimize ExportLc

test if there is anything to save before opening the file

generalized ExportLcField to all element types

make Export_LcField also work with SimplexBase

- removed the quads from the simplex trees (finally...)

  **warning**

  this is a pretty big patch that touches a lot of different files. I
  tried my best to update all the things that needed to be updated,
  but I probably forgot some things... Please test! (especially the
  export routines in obscure formats like SMS, Gref, etc., as well as
  the extrusion code)

- added second order edge vertices for hexas, prisms and pyramids
  (drawing not done yet)

- added sanity check for number of values in post-pro parsed file
  format

- merged all mesh printing/reading routines in Print_Mesh.cpp and
  Read_Mesh.cpp

- cleaned up the statistics code

fix exportLcField for lines and quads

- add GUI for exporting characteristic length fields
- error->warning if lc <= 0
- don't enable POLYGON_OFFSET_FILL for 3D isos

typo

some more bgmesh cleanups

Small corrections for ONFILE background meshes:

- should now work reliably interactively (and not only the first time
  the view is applied as a background mesh)

- fixed some memory leaks

Update copyright notice

Fix whitespace in copyright headers

Indented all source files using utils/gmshindent

Updated copyright