Soft logout: Actually show the page

[turt2live]

Using designs from #10224 (comment)

Conditions: when the user receives a 401 with soft_logout: true, redirect to page.

Page requirements:

• Sign in button goes to login (prefill left as Soft logout: Rehydrate session from soft logout page #10236)
• Clear data clears data
• Logout section conditional on key backup status
• Key export if needed (https://github.com/vector-im/riot-web/issues/9444 / Soft logout: Export e2e keys button? #10249)

[nadonomy]

As per #10224 (comment), we should also action:

The client knows whether or not (a) the user had server side key backup enabled (b) if they did, whether any local keys aren't backed up. Therefore, there are now 2 variants for when a user has all their keys backed up or not.

[turt2live]

Mostly as a note to myself:

@lampholder had a conversation with M&A about the key backup/export button. tldr is it won't be there now. Updated comps coming later.

[nadonomy]

@turt2live Zeplin is now updated based on the latest requirements: https://zpl.io/a89QL5x