Platform: Ensure classes match their header filename

Also drop some unused files.

Renamed:
- `platform/iphone/sem_iphone.h` -> `semaphore_iphone.h`
  (same for `osx`)
- `platform/uwp/gl_context_egl.h` -> `context_egl_uwp.h`
- in `platform/windows`: `context_gl_win.h`, `crash_handler_win.h`,
  `godot_win.cpp`, `joypad.h` and `key_mapping_win.h` all renamed to
  use `windows`. Some classes renamed accordingly too.
- `EditorExportAndroid` and `EditorExportUWP` renamed to
  `EditorExportPlatformAndroid` and `EditorExportPlatformUWP`
- `power_android` and `power_osx` renamed to `PowerAndroid` and
  `PowerOSX`
- `OSUWP` renamed to `OS_UWP`

Dropped:
- `platform/windows/ctxgl_procaddr.h`

platform/uwp/power_uwp.h

@@ -28,8 +28,8 @@
 /* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
 /*************************************************************************/
 
-#ifndef PLATFORM_UWP_POWER_UWP_H_
-#define PLATFORM_UWP_POWER_UWP_H_
+#ifndef POWER_UWP_H
+#define POWER_UWP_H
 
 #include "core/os/dir_access.h"
 #include "core/os/file_access.h"
@@ -53,4 +53,4 @@ public:
 	int get_power_percent_left();
 };
 
-#endif /* PLATFORM_UWP_POWER_UWP_H_ */
+#endif // POWER_UWP_H