[IMP] website: simplify website menu

Some apps, once installed, automatically create a menuitem in website.
What complexify the UI and create useless menu withtout plusvalue.

It is not because you install livechat to make support online, that you want
a link in your menu to show stats e.g.

Now we remove the default menu created, and help user to find it when he create
a link. The autocomplete suggest most of the main App's controllers

task-2189613

closes odoo/odoo#49081

Related: odoo/enterprise#9733
Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com>