Move the backup function to the settings page

[quazar-omega]

(Related to #128)
I was looking for the feature to export he data and initially couldn't find it, I clicked on the question mark icon just out of curiosity not expecting to find it there, I think it'd make more sense to keep it with the rest of the settings for better discoverability

[ncosgray]

You're so right! I'm not entirely sure how the export/import buttons ended up on the About page instead of on the Prefs page. I will make this change.

Thank you so much for your interest in Cuppa. :)

[quazar-omega]

Thank you for the handy app, I've used it so much now to get the timing right on my teas!
And happy to hear you agree on the suggestion