add umu integration

[michaelBelsanti]

Currently, Butler/Itch has very basic support for launching games through wine. It doesn't offer configuration options, simply using the default wine prefix and running the game executable through wine.

umu-launcher makes running games using Proton pretty simple and includes a database of game fixes. There aren't currently any itch games, but it supports them, so any fixes found could be easily added and available to anyone running a game through it.

A simple implementation would involve checking if umu-launcher is installed and if so, using that as the wrapper instead of wine. The main change that would be needed to use umu would be creating a directory for per game prefixes, rather than using the default wine prefix.

Related: itchio/itch#3085

[michaelBelsanti]

I plan to start experimenting with this soon.

[leafo]

Just digging through older issue and I think this is a good idea, there's a handful of changes we should be making to improve our wine support. umu seems like a good option for integrating with proton