Extract keys and history from web client

[Kagami]

It should be several ways to extract keys and history from the web client because there is always a possibility that domain/hosting would be blocked for some reason (it's centralized after all):

• Generally users should be encouraged to use their own hosted version of web client (i.e. consider public cilents as demo-only or when it's the only way)
• There should be the option to export keys/history in the client
• It is also good to have some scripts which can parse browser profiles and extract local storage/indexed db data for the given domain (helps if client doesn't have backup)