Different default emulator core per arcade system (fbneo and mame)

[kitwalker14]

Is your feature request related to a problem? Please describe.
It would be very handy if we could define the default core per arcade system

Describe the solution you'd like
A way to delineate library paths to have a different default core per path (I have 2 folders, 1 for fbneo, 1 for mame)

Describe alternatives you've considered
Not sure how to achieve this currently as the arcade system can only have 1 core as default

Additional context
N/A