Nav: Added ImGuiNavInput_KeyMenu aside from ImGuiNavInput_PadMenu as it is one differenciator between pad and keyboard that's very annoying with the keyboard.

Remove the move/resize behavior that appears than holding the button for a while. (#787)

imgui.h

@@ -640,6 +640,7 @@ enum ImGuiNavInput_
     ImGuiNavInput_PadFocusNext,     // prev window (with PadMenu held)              // e.g. R-trigger
     ImGuiNavInput_PadTweakSlow,     // slower tweaks                                // e.g. L-trigger, analog
     ImGuiNavInput_PadTweakFast,     // faster tweaks                                // e.g. R-trigger, analog
+    ImGuiNavInput_KeyMenu,          // access menu                                  // e.g. ALT
     ImGuiNavInput_COUNT,
 };