[FIX] mail_tip: prevent blank webclient
[ADD] pad: new etherpad plugin to remove autofocus

In the form views where the pads are used, Etherpad-lite automatically
focus on the pad content, even if the user has already started to type
into another field.

This behavior is quite annoying for "quick changes", so we provide a
(very tiny) plugin for Etherpad-lite that will prevent this autofocus.

Detailed installation instructions are also included.
[IMP] account, account_analytic_analysis: fix labelling incoherences

- account: this change aims to keep the same labels on form and list views
- account_analytic_anlysis: correct search field
[IMP] website: correct page hierarchy for comparison snippet
[IMP] website_sale: Show error message if VAT number, Email is invalid.