Unintentional logout should allow key backup

[TheJJ]

Description

When, for whatever reason, one is logged out (password change element-hq/element-web#2671, funny security incidents, ...), riot-web should provide the possibility to download the E2E keys.

Steps to reproduce

• Use Riot with E2E-Rooms
• Wait to be logged out
• Discover that you did not set up/create key backup etc
• E2E data can't be exported conveniently since one is logged out

Steps to fix

• Add some UI displayed after an unintentional logout to export E2E keys

[exuvo]

With the recent matrix.org security breach I too was forced to re-login, but the desktop client then forgets all the room keys which is weird as those should already be stored locally at that point?

Describe the solution you'd like
Allow for exporting keys before the client does a forced logout.

Workaround
I was forced to restore my riot data directory from backups and restart riot with internet disabled (which keeps the client from logging me out instantly) to be able to export the E2E room keys.

[xloem]

Note that if you have no backup an individual with experience in data-recovery or a tool such as autopsy should be able to recover the keys, if the computer is not left powered on for too long after the incident.