Remapping: Documentation and defaults update + add option to use a unified config (#2302)

* Add a toggle to use unified or per-game configs, and add a deadzone example to the default config

* Add a checkbox to toggle config type

* clang

src/common/config.h

@@ -43,6 +43,8 @@ std::string getBackButtonBehavior();
 bool getUseSpecialPad();
 int getSpecialPadClass();
 bool getIsMotionControlsEnabled();
+bool GetUseUnifiedInputConfig();
+void SetUseUnifiedInputConfig(bool use);
 
 u32 getScreenWidth();
 u32 getScreenHeight();