Add average sign and percent in mc_generic

Added an access to the percent done and to the
average sign after collect_results is called

  modified:   triqs/mc_tools/mc_generic.hpp
gf : SAVING WORK ...
gf : solve pb slice/n_pts
gf: Fix mesh product index bug, add on_mesh friend.
arrays : fix bound_check for slices

-Fix also details in a few tests, corresponding...
gf : simple tests ok
cmake : stop compile python test of array

- boost python to be removed.
gf : work on demo...
gf_local : fix assert in old gf for debug mode
utility : add value_view class

- To handle a value & the corresponding view
in class. Analogous to array/ array_view
for simple object...
arrays : remove assert py_obj in raw_copy

- To be rechecked : Is it really correct ?
gf : work on C++ and python
Fix a missing friend class in value_view.hpp

  modified:   triqs/utility/value_view.hpp
Fix problem when using existing boost

Because things were not in the good order in the main CMakeLists.txt
the pytriqs/boost link was not created on the first call of cmake
when an existing boost was used. It appeared on a second call though.

  modified:   CMakeLists.txt
Improve some aspects of documentation

Did an iteration over the installation part.

  modified:   doc/user_manual/install/Ubuntu.rst
  modified:   doc/user_manual/install/dependencies.rst
  modified:   doc/user_manual/install/wien2k_inst.rst
  modified:   doc/user_manual/wien2k/Ce-HI.rst
Merge branch 'master' into 1.0
Fix in main CMakeLists.txt
Merge branch 'master' into 1.0
gf : add pickle for gf, tail, ...

- using copy_reg for the gf_generic
so it is done once for all in upper class.

- for tail, use boost::serialize reduction from C++.

- for mesh, simple reduce from parameters.
Fix small plotting issues with gf

  modified:   Base/gf/local/gf_generic.py
  modified:   Base/gf/local/gf_imfreq.py
  modified:   Base/gf/local/gf_imtime.py