[ADD] Website KeyCDN integration guide
[IMP] stock_account: stock journal in multicompany

Restrict the property_stock_journal to the main company only. This avoids errors in multicompany when the stock journal of the main company (getting an error company mismatch) is used instead of a more useful message explaining the missing stock journal.
Fixes #3251
[IMP] website_sale : Don't show shipping address when only services are into shopping cart.