[ADD] Module  help_online

# User documentation using the website module

*This PR follows the positive feedback from members of the community in response to a [post] (https://www.odoo.com/groups/community-59/community-8982559?mode=thread&date_begin=&date_end=) of Stéphane Bidoul on the mailing list.*

> People interested in providing user documentation in their projects may want to look into a module we developed to create online help.
> 
> The principle is rather simple: a help icon appears on form and list views. The icon shows a help page for the model if it exists or let the user with appropriate rights create a new help page themselves. Help pages are created with the v8 website editor.
> 
> We have a few ideas to improve it, but the module is already functional in its current state.