Accessibility proposal: removing extra H1s from the page

[mleduc]

@CharpentierLucas

Only use one H1 per page, except for user generated content.
This would mean that we do not update the rendering of user’s content, but we should change:

• current UI elements using H1s such as panels
• default page contents with H1s, such as the Home page, to replace every = title = with == title ==

+1

Do you also want to make it a best practice when writing pages on (*.)xwiki.org ?