ReplayItem class could use a refactor

[Wesmania]

The ReplayItem class has logic and widgety stuff mixed together, and it special-cases many mods in huge methods. We can probably factor out the logic into some Replay class and maybe make subclasses for mods we special-case, with a factory class to create replays depending on the mod.

[Wesmania]

I made some initial work on that in Wesmania/client@0e521ee9bdb49f6e0d2546d18aa3480e0efbab84. I think a good step towards cleaning up the code further would be replacing the mess of HTML with some Qt widgets. Might be something up your alley @GrotheFAF.

[GrotheFAF]

is that done, with your refactor?

[Wesmania]

I think my refactors didn't touch the replay tab much beyond splitting up the main class, so I think not yet. Now that we have a game model class, it should be a bit easier, too.