Refactor imgui backend code into imgui drivers for gl, vk, dx9
Generic GraphicsContext interface for gl/vk/dx9 contexts
Simplify graphics api switching code
dx9, gl(sdl): set swap interval based on monitor refresh rate.
Fix per-game settings (Issue #115)
Automatic load/save state (Issue #173)
Reload Naomi/AW BIOS after per-game settings are loaded to allow
per-game BIOS region. (Issue #96)
Restrict Soul Reaver widescreen cheat to the EU version (Issue #188)
Disable UI elements for overridden settings
Clean up/simplify legacy Naomi ROM loading