Write a plug-in system for EmuGUI

[Tech-FZ]

So far, EmuGUI is not the most modular application you can get. The only modular thing is the fact that you can choose the QEMU binaries you want. However, a plug-in system can partially fix things. They could be categorised as such:

• Additional VM specs: Stuff that EmuGUI can't utilise by itself. Must be supported by QEMU. Too complicated and probably not necessary.
• Additional options for certain stuff: Could add CPUs, network cards, whatever, if QEMU supports it, but EmuGUI doesn't on its own.
• VM assistance plug-ins: When starting the VM, EmuGUI would automatically open them. See issue Make it easier to switch ISO and virtual floppy files #42 for an example.