[ADD] JS widgets reference documentation

Also fixed Widget#alive's behavior and tested it
[ADD] port webclient RPC doc from web/doc
[FIX] sphinx 'project' value

The project name automatically gets the release and the literal string
"documentation" appended by default (and "html_title" can be set to generate a
title differently), so having "documentation" set in the project variable
duplicates it in the page title.
[FIX] JS tutorial
Merge pull request #2375 from odoo-dev/8.0-webclient-doc-xmo

Port web client tutorial fully (-ish), improve JS doc.