Make the Wiki home page logo point to the Wiki's home instead of hardcoding it Main.WebHome

We can currently change the homepage field of the wiki descriptor either directly (Wiki Index > edit) or from within a wiki's Administration (Administration > Wiki > Descriptor), however the setting is not really used by the UI. Only the Wiki Index uses it right now to determine the homepage of a wiki in the list. It should also be used when clicking a wiki's logo for example and many other places.

Example workflow reused/extracted from a previous issue (XWIKI-11746)

1. Go to the Wiki Index (WikiManager.WebHome)
2. Click on Edit from the Actions column for the new wiki
3. Click on the blue Edit button
4. Change the "HOME PAGE:"; for ex. use Sandbox.WebHome
5. Go back to the Wiki Index
6. Click on the wiki name -> you're taken to Sandbox.WebHome
7. Click on either the XWiki logo from the top left or on the wiki name from the top bar: 2nd issue -> you're taken to Main.WebHome