Win32: Use wide strings to parse most command-line arguments.

It doesn't make much sense to parse them as ANSI/ASCII anymore, since we use Unicode now. In addition, it's currently not possible to load states, games, or configuration inis from paths with Unicode glyphs in them.  I left NativeApp mostly unchanged due to its cross-platform nature, making minimal additions where needed (should really convert the argv stuff to C++ strings, but that's for another day).
EmuThread.cpp needs to see it, somehow. I'll just add an extern prototype.