Improve `edit page` UX

[owi92]

There are a couple of points that came up in the recent design review:

• [ ] It's not obvious how to switch between the "edit page" and regular page... pages. Maybe we can add an "edit" button that links to the "edit page" page next to the regular page heading.

• [ ] Being on the "edit page" page, it's not obvious to the user that they can edit page content on that page. This could be improved by removing the page title from the heading, so it always says "Edit page". Otherwise that might be overlooked, especially with longer titles.

• [ ] It's not obvious to the user that any changes/edits they make are automatically applied to the regular page they are editing.

The last two points could be addressed by adding a note at the top of the page. Something like "Here you can edit the page content. Anything saved here is automatically applied to the real page." (Well, "real page" might not be the best expression. As always, wording and anything else is open for discussion)

[LukasKalbertodt]

One idea I had was sth like this:

• It would still be the edit route (i.e. /~manage/realm/...)
• The title would just be the page title
• There would be a big obvious banner that explains one currently edits this page. It can also explain that all changes are immediately saved. It can also have an X to exit the editing mode.
• The blocks would look like normal blocks, so that the page looks exactly like normal. Only when hovering over a block would the typical edit buttons (and maybe the border around the block) appear. Although mh... what about devices without hover?

So yeah, just throwing this out there.