Encouage or automate backup before update

[borpin]

Following on from a discussion https://community.openenergymonitor.org/t/help-fatal-error-after-emonpi-update/9681 where a user updated then had issues with their system, I suggest that users are encouraged to backup their instance before performing updates.

Even better would be a mechanism to do a backup automatically before an update is attempted. This could perhaps be to a zip file that is then downloaded to the local machine.