VideoConfig: Rename Separation to Depth and update descriptions.

More accurate since it's not a real IPD and Nvidia also calls it depth.

Source/Core/Core/ConfigManager.cpp

@@ -81,8 +81,8 @@ static const struct
 	{ "FreelookZoomOut",      83 /* 'S' */,       4 /* wxMOD_SHIFT */ },
 	{ "FreelookReset",        82 /* 'R' */,       4 /* wxMOD_SHIFT */ },
 
-	{ "IncreaseSeparation",  0,                   0 /* wxMOD_NONE */ },
-	{ "DecreaseSeparation",  0,                   0 /* wxMOD_NONE */ },
+	{ "IncreaseDepth",       0,                   0 /* wxMOD_NONE */ },
+	{ "DecreaseDepth",       0,                   0 /* wxMOD_NONE */ },
 	{ "IncreaseConvergence", 0,                   0 /* wxMOD_NONE */ },
 	{ "DecreaseConvergence", 0,                   0 /* wxMOD_NONE */ },
 

Source/Core/Core/CoreParameter.h

@@ -54,8 +54,8 @@ enum Hotkey
 	HK_FREELOOK_ZOOM_OUT,
 	HK_FREELOOK_RESET,
 
-	HK_INCREASE_SEPARATION,
-	HK_DECREASE_SEPARATION,
+	HK_INCREASE_DEPTH,
+	HK_DECREASE_DEPTH,
 	HK_INCREASE_CONVERGENCE,
 	HK_DECREASE_CONVERGENCE,