[Suggestion] Emulator runners with different versions of the emulator

This could be set up similar to managing Wine versions. Some emulators like Dolphin, DeSmuME, Citra and PCSX2 often have development/nightly builds that are far beyond their latest stable build in feature scope, game compatibility, performance tuning, etc. It would be great to have a way to have Lutris manage these versions, especially if like Wine versions, we could set the emulator version per game if a game works better under a certain version.

Or if not set up like Wine versions, just being able to choose between either using the latest stable version, or using a development/nightly build would be a huge improvement. Most of these have a buildbot or github or something similar to pull the latest development versions from, rather than Lutris needing to be updated with which version it supports periodically.