Add mame to Gaelco emulators list

Hi!

At this point in time the emulation of Gaelco system requires the use of mame together with Demul. Demul does not support the full library of Gaelco games, while mame (current) emulates them really well, except some of the most important ones, where Demul is necessary.

So it's like fifty/fifty.

Here's the video of a guy setting up batocera: https://www.youtube.com/watch?v=50guFlpxZ-c - and as you can see, he's juggling between demul, current mame and older mame versions. From my experience, older mame versions are not needed, it's just he's probably having some older romsets. There were changes to these roms in 0.253, I believe? Or something like that. Anyway, Demul-old-gx-core + current romsets (>=0.260?) + lr-current mame version should be enough.

As of now, Retrobat is configured to use Demul with old dx11 core only. I'd like to suggest adding mame to the list of emulators for Gaelco in es_systems.cfg.