Handle the home icon in breadcrumbs as main wiki webhome and display current wiki

See XWIKI-12407 for more information on the original proposal.

What is left to be done is to treat the 'home' icon that is displayed in the breadcrumbs as the main wiki's homepage and not the current wiki's.

Also, the current wiki should be displayed as first item after the 'home' icon, when displaying the breadcrumbs of a document inside a subwiki.

Note that we must consider the wiki's type before we do both operations above, since for a farm subwiki we probably don`t want this new behavior and prefer the old one which is to use the current wiki's homepage as link to the home icon and not to display the current wiki in the breadcrumbs, to preserve isolation.