Simplify Backup Page

[rolznz]

Currently the backup page is scary and complicated (requires saving multiple things - see #750).

We could split it into Alby Account vs no Alby Account components to reduce the conditionals.

No Alby Account could have a button to download SCBs (or somewhere else, e.g. on the node page which is shown whenever a new channel is opened and user does not have backups for that channel yet).

Alby Account version can be improved when we implement VSS and remote backup of NWC data.

[jpl-btc]

Just an idea: For no-Alby Account Hubs, whenever a new channel is opened, include a prompt or a warning somewhere reminding the user to download the SCB (Static Channel Backup) file. It might be a little annoying for power users, but increases the user's security by pushing him/her to download the necessary backup files after each new channel, as it should be, and they may better understand the convenience of having an Account and a subscription.

[rolznz]

This could also be good for Alby Account users who still want to save SCBs locally ("what happens if alby disappears" question).

[rolznz]

I think this is mostly a technical task as the guide has already been improved significantly, and is linked from this page.

1. Split the page up into separate components for Alby Account vs no Alby Account to reduce conditionals
2. Create new issue for allowing to download backups directly from the Alby Hub UI for users without Alby accounts (initially put it on the backup page, since more logic is required to know if the user has made a backup of their most recent channel)