[SàT dev] [EN] Reorganisation of Libervia's file hierarchy

[Adrien]

Hi,

the organisation of Libervia's files hierarchy has been changed for a 
more intuitive and flexible "tree". It now uses the "src" directory (as 
it's done in sat).

Below the changeset description:

/!\ reorganize all the file hierarchy, move the code and launching 
script to src:

     - browser_side                --> src/browser
     - public                      --> src/browser_side/public
     - libervia.py                 --> src/browser/libervia_main.py

     - libervia_server             --> src/server
     - libervia_server/libervia.sh --> src/libervia.sh

     - twisted                     --> src/twisted

     - new module src/common
     - split constants.py in 3 files:
         - src/common/constants.py
         - src/browser/constants.py
         - src/server/constants.py

     - output --> html (generated by pyjsbuild during the installation)
     - new option/parameter "data_dir" (-d) to indicates the directory 
containing html and server_css

     - setup.py installs libervia to the following paths:
         - src/common --> <LIB>/libervia/common
         - src/server --> <LIB>/libervia/server
         - src/twisted --> <LIB>/twisted
         - html --> <SHARE>/libervia/html
         - server_side --> <SHARE>libervia/server_side

     - LIBERVIA_INSTALL environment variable takes 2 new options with 
prompt confirmation:
         - clean: remove previous installation directories
         - purge: remove building and previous installation directories

You may need to update your sat.conf and/or launching script to update 
the following options/parameters:
     - ssl_certificate
     - data_dir

Feel free to ask any question or share your opinion if you think that 
something should be changed.

Best regards,
Adrien