WinRT: file naming and placement cleanup

- moved SDL_WinRTApp.* from src/video/windowsrt/ to src/core/winrt/, and renamed them to SDL_winrtapp.* (to mimick case-sensitivity used elsewhere in SDL)
- renamed all "windowsrt" directories (in src) to "winrt", as the shorthand name is used more often (and, IMO, "WinRT" != "Windows RT", not entirely at least)

src/core/winrt/SDL_winrtapp.cpp

@@ -13,7 +13,7 @@ extern "C" {
 #include "SDL_main.h"
 #include "SDL_stdinc.h"
 #include "SDL_render.h"
-#include "../SDL_sysvideo.h"
+#include "../../video/SDL_sysvideo.h"
 //#include "../../SDL_hints_c.h"
 #include "../../events/scancodes_windows.h"
 #include "../../events/SDL_mouse_c.h"
@@ -22,8 +22,8 @@ extern "C" {
 #include "../../render/SDL_sysrender.h"
 }
 
-#include "SDL_winrtvideo.h"
-#include "SDL_WinRTApp.h"
+#include "../../video/winrt/SDL_winrtvideo.h"
+#include "SDL_winrtapp.h"
 
 using namespace concurrency;
 using namespace std;

src/video/winrt/SDL_winrtevents.cpp

@@ -26,7 +26,7 @@
 
 #include "SDL_winrtvideo.h"
 #include "SDL_winrtevents_c.h"
-#include "SDL_WinRTApp.h"
+#include "../../core/winrt/SDL_winrtapp.h"
 
 extern SDL_WinRTApp ^ SDL_WinRTGlobalApp;
 

src/video/winrt/SDL_winrtmouse.cpp

@@ -29,7 +29,7 @@ extern "C" {
 #include "../SDL_sysvideo.h"
 }
 
-#include "SDL_WinRTApp.h"
+#include "../../core/winrt/SDL_winrtapp.h"
 #include "SDL_winrtmouse.h"
 
 using namespace Windows::UI::Core;

src/video/winrt/SDL_winrtvideo.cpp

@@ -38,7 +38,7 @@ extern "C" {
 #include "SDL_syswm.h"
 }
 
-#include "SDL_WinRTApp.h"
+#include "../../core/winrt/SDL_winrtapp.h"
 #include "SDL_winrtvideo.h"
 #include "SDL_winrtevents_c.h"
 #include "SDL_winrtmouse.h"