recommend add core switch function

[makejohn]

Recently, I found out that some 'nes' games won't open with 'nestopia' core, that issue exited in OpenEMU too which is an emulator on mac, the default core that openEMU use is also 'nestopia', but it allows you to switch to 'FCEU' core which fixed the game won't open problem, so, could you pls add a core switch function? or could you pls tell me how can i switch the core myself

[lonkelle]

@makejohn What games have you experienced this with so far; I'd like to test this out myself. :)