Allow changing the order of facts in Overview

[jtojnar]

Currently, the overview uses ORDER BY DATE(start) DESC, TIME(start) ASC. For many users, simple ORDER BY start DESC or ORDER BY start ASC will be more natural. We should allow them to customize it.

[floi]

It looks like facts per day aren't actually ordered by start, but by their database id/order they were saved in. There is a comment in the code suggesting that ordering by fact start is the intended behavior, though.

I'm interested in trying my hand at this, but making the order configurable entails a UI decision I don't feel qualified to make – should this be set via the preferences or by, say, a button or combobox in the header bar?

[floi]

After giving this some more thought, I think that users might not want to change the order all the time so that adding this to the preferences makes more sense.