Separate emulation support as add-ons

[JosefNemec]

Feature description

Emulator profiles should be separated and made available as add-ons to:

• make it easier to add support for new emulators without need to release new program update
  • the same for updates
• easier support for things like arcade support #2407
• more flexibility to emulators that require special care related to game startup or import (like RPCS3)

This should be done prior to #2407. It would also probably make sense to wait for #593 to be completed since it could be a mess to manage all these emulator add-ons without it.

Screenshots

No response

[Lucoshi]

I want that for DOS and MAME.