Handle secondary and tertiary sorting

[apobrt]

This PR aims to adjust the sorting adding the logic of the secondary and, in some cases, tertiary sorting. It closes #181

The main logic is that the books are sorted :

• firstly, by the selected sorting option (e.g. author)
• when the first option is not discriminant (e.g. multiple books have the same author), they are sorted by release date
• if also this is not sufficient (because they are released in the same year or the information is not present), they are sorted by title

This should handle most of the cases, even some edge cases like the comics, when we would need the full release date (we only store the information of the publication year). It obviously fails when the titles are not correctly sortable.

P.S.: this is my very first PR ever, so let me know if I miss something, or I have made something wrong

[mateusz-bak]

Great! Can you fix the merge conflicts? I looked at them and they should not cause too much trouble.

At the first glance it look reasonable, I will test the implementation when you fix them.

[apobrt]

Hi, I think I've done!

[mateusz-bak]

Great! Looks good, tested just now.

Merging and thanks 🎉