add SSL support to VTKWeb server

New command-line arguments allow us to serve VTKWeb content
over secure websockets.

Change-Id: Ieb5bb9c5a4387bd9ec6c738546f3622480b7b2f1
Merge topic 'vtkweb_ssl' into master

14071140 add SSL support to VTKWeb server
Redesign "vtkGhostLevels" arrays and related ghost functionalties.

 -The semantics of each unsigned char in the ghost arrays changes:
  Instead of storing a numeric value representing how far a cell is
  from the boundary, it is now a bit field specified by
  vtkDataSetAttributes::CellGhostTypes and
  vtkDataSetAttributes::PointGhostTypes.  The bit field is consistent
  with VisIt specs.

- Previously, filters strip all ghost cells they request from upstream
  before finalizing the output. This is no longer done.

- vtkUniform grids previously supports blanking through member arrays
  vtkUniformGrid::CellVisibility and
  vtkUniformGrid::PointVisibility. These arrays are removed and the
  blanking functionality are supported through the new ghost arrays
  instead.

- the "vtkGhostLevel" arrays for cell and point data are renamed by
  vtkDataSetAttributes::GhostArrayName().

Change-Id: If5ff516c0fb0b321aa9e0fcc8cf7e74f05e2b250