Allow multiple folders for one handler

[Miss-Inputs]

Currently, ROMniscience only allows one folder for one handler. This is just because I store my ROMs like that (one system and one folder), and I figure most people do that too. But what if they don't? Especially when you have systems that you might want to group together, like Wii and WiiWare, which I don't put in the same folder but some people might, or maybe Megadrive and Mega CD once I get the latter working, or... whatever. I don't judge. And one of my software philosophies is that I don't judge the user on what weird shit they want to do.

Anyway, this shouldn't require too much thought on the backend, just as long as the settings file is backwards compatible (who knows, maybe someone who isn't me uses this program and I just don't know that yet). Configuring it in the GUI in a user-friendly way is the tricky part. As a last resort I guess we just have folders separated by | or ;, but that's ugly and makes the behaviour of the "choose folder" button non-obvious and confusing.

[Miss-Inputs]

For reference, these are the handlers (including CD-based ones that I'm going to implement sooner rather than later) that sort of go together and so you might reasonably expect a user to keep them in the same folder, but maybe they might not and so at the moment they'd have to be separate:

GBA + e-Reader
Atari Jaguar + (Jaguar CD)
MSX + MSX2
PC Engine + (Turbografx-CD)
Megadrive + 32X + (Mega CD) + arguably Pico
Game Gear + Master System (kinda? Nearly same hardware, and all emulators that can do one can do the other)
Wii + WiiWare + (Wii homebrew) (maybe Gamecube as well? I'm sure there are people who have a single "Dolphin folder")

PC Engine and Game Boy are two handlers in particular where this issue could become an issue, because maybe people like to put their Supergrafx and GBC ROMs in a different place. Also N64 where I've included N64DD, come to think of it.

Heck, maybe people like to have different regions in a different folder. There's probably people who have a SNES folder and a Super Famicom folder. Who knows.

For what it's worth, you can set two handlers to the same folder, but it might not be obvious to the end user that you can do that, and so maybe they assume you can't, because there's a lot of software out there that asks you for multiple folders and complains when you use the same folder twice for different things.