Backup shouldn't restore outdated data

[darekkay]

Some widgets, like the Cryptocurrency or the GitHub widget, rely on up-to-date information. When the data is exported (settings menu) and imported later, it will contain outdated information. This should be solved by either:

• Excluding certain data from the export, or
• Excluding the data when it's being imported

A generic approach to define excluded paths per widget is required.

An alternative or addition is to mark outdated data somehow (e.g. an exlamation mark) or placing "last updated" label somewhere.