Separate emulator_command_lines from emulator_info

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It's the only way for future refactoring to work without circular imports… don't import it from there, import it from roms or whatever.

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Given the amount of issues I ended up referencing here, I should probably think of something. Maybe having it be a dict of existing emulator name > function can work, and then roms.py or whoever else needs it just looks it up? Then I don't have to repeat myself by rewriting the emulator name in snake_case each time.

Only problem is what I've said up there on line 4 (apparently at some point in time):
#It would be infeasible to create a function in emulator_command_lines for everything, I guess
Too bad, me! You're gonna have to do it now. Unless… I might need to do #135 at the same time, and then think of some "simple command line" thing? Which I was going to think of anyway.

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…There is a simple solution of just taking the functions that we put in EmulatorInfo right now, and referencing somewhere else

Emulator Name -> command_lines.blah
Mednafen module -> None if it just uses mednafen_module_callable with module name (or it just doesn't go in the dict)
MAME driver -> command_lines.mame_blah or mame_driver_callable

Make it look interesting later, but putting it somewhere else isn't necessarily creating more work for myself. It just changes how one might approach #135

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So I avoided the problem but I kinda want to do the above anyway, just to make one's life easier in the future, especially with #135 involved. This requires the get_mame_driver_command_line/get_standard_emulator_command_line/whatever to go in roms.py (and also pc.py) though since the BaseEmulator objects don't know their own names