[ADD] website_version: website versioning and ab testing

addons/base_setup/res_config_view.xml

addons/website/__openerp__.py

addons/website/controllers/main.py

addons/website/data/demo.xml

addons/website/models/ir_http.py

addons/website/models/ir_ui_view.py

addons/website/models/website.py

addons/website/static/src/js/website.ace.js

addons/website/static/src/js/website.editor.js

addons/website/static/src/js/website.snippets.editor.js

addons/website/views/website_templates.xml

addons/website/views/website_views.xml

addons/website_version/__init__.py

addons/website_version/__openerp__.py

addons/website_version/controllers/__init__.py

addons/website_version/controllers/main.py

addons/website_version/data/data.xml

addons/website_version/data/demo.xml

addons/website_version/models/__init__.py

addons/website_version/models/experiment.py