better gestion of remote messages ("a la getdp")

finished up first pass at remote view management:

* interactive stuff is now almost feature-complete (including
  multi-step, axes and adaptive refinement)

* plugins can now be executed on remote views

* renamed GmshRemote->ConnectionManager & GmshDaemon->GmshRemote

added some more topological infos in high order elements (useful for DGM,
still have to be tested)

serialization of options)

renamed most gmsh* classes

also transfer vector arrays

(we should design a small container atop the va to store the additional
info we need to transfer: min/max, bbox, timeval)

send/receive vertex array over socket ok

added GmshSetBoundingBox

refactored the solver code (new GmshRemote class to handle all remote
executions, including solvers)

made client startup non blocking + prepare SINFO refactoring