Configuration files

Do not merge - this is a preliminary PR for discussion.

As of now, incorporates Dolphin's INI code for a configuration system. So far, handles for input controls have been added, but they haven't been hooked yet into the parts of code that use them. 
All the GUI stuff should probably be wrapped within a Citra resp. CitraQt namespace to avoid having those redundant GLFW_ prefixes, but that's out of scope for this PR, I guess.