Add support for custom Title Sorting

[hausofwong]

Currently the games collection list ignores the sort_title key that allows you to add a custom override title to help with sort order. e.g Games with roman numerals tend to be in the wrong list order.

It also supports sort-by and sort_name as well.

Fixes #19

[hausofwong]

After further testing I spotted that 'sort_title' was breaking the order direction functionality. Changing it to the actual Pegasus API property fixes that.

[Christoffer-Cortes]

Nice change! I was gonna look into doing this myself but then I saw this PR. I've verified that it works and I'm gonna use these changes on my fork. :)

[djfumberger]

Great, thanks!